H. Berger - Academia.edu (original) (raw)
Papers by H. Berger
[sub 4]Cl[sub 2] with frustrated geometry](https://attachments.academia-assets.com/50768402/thumbnails/1.jpg)
](Low Temperature Physics, 2008
The magnetic and magnetoresonance properties of a new single-crystal compound Ni 5 ͑TeO 3 ͒ 4 Cl ... more The magnetic and magnetoresonance properties of a new single-crystal compound Ni 5 ͑TeO 3 ͒ 4 Cl 2 are studied. Measurements of the magnetization and magnetic susceptibility of the crystal in a wide temperature range ͑5 -300 K͒ make it possible to conclude that Ni 5 ͑TeO 3 ͒ 4 Cl 2 is a quasitwo-dimensional antiferromagnet with the easy magnetization axis a * directed perpendicular to the crystallographic plane bc and a magnetic ordering temperature T N Ϸ 21 K. Resonance measurements at 4.2 K in wide range of frequencies ͑25-105 GHz͒ and magnetic field ͑up to 200 kOe͒ permit us to obtain the frequency-field dependence of the AFMR spectrum for a field applied along the easy magnetization axis a * . It is shown that a magnetic field directed along the antiferromagnetic axis ͑H ʈ a * ͒ induces a magnetic phase transition of the spin-flop type, which is found to occur at H sf Ϸ 120 kOe. The magnetic resonance experimental data are described qualitatively in the model of a biaxial antiferromagnet.
Spectroscopic signature of magnetic exchange with high resolution RIXS
New Journal of Physics, 2008
By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the... more By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the fermiology of 2H transition metal dichalcogenide polytypes TaSe 2 , NbSe 2 , and Cu 0.2 NbS 2 . The tightbinding model of the electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate the Lindhard function (bare spin susceptibility), which reflects the propensity to charge density wave (CDW) instabilities observed in TaSe 2 and NbSe 2 . We show that though the Fermi surfaces of all three compounds possess an incommensurate nesting vector in the close vicinity of the CDW wave vector, the nesting and ordering wave vectors do not exactly coincide, and there is no direct relationship between the magnitude of the susceptibility at the nesting vector and the CDW transition temperature. The nesting vector persists across the incommensurate CDW transition in TaSe 2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu 0.2 NbS 2 the nesting vector is present despite different doping level, which lets us expect a possible enhancement of the CDW instability with Cu-intercalation in the Cu x NbS 2 family of materials. PACS numbers: 71.45.Lr 79.60.-i 71.18.+y 74.25.Jb
Physica C: Superconductivity, 2007
The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects... more The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects in angle resolved photoelectron spectra (ARPES) of Bi 2 Sr 2 CaCu 2 O 8+d is addressed. We show that the nonmagnetic Zn atoms have much stronger effect both in nodal and antinodal parts of the Brillouin zone than magnetic Ni. The observed changes are consistent with the behaviour of the spin resonance mode as seen by inelastic neutron scattering in YBCO-123. This strongly suggests that the ''peak-dip-hump'' and the ''kink'' in ARPES on the one side and neutron resonance on the other are closely related features.
Physical Review B, 2007
A novel Bloch-waves based one-step theory of photoemission is developed within the augmented plan... more A novel Bloch-waves based one-step theory of photoemission is developed within the augmented plane wave formalism. Implications of multi-Bloch-wave structure of photoelectron final states for band mapping are established. Interference between Bloch components of initial and final states leads to prominent spectral features with characteristic frequency dispersion experimentally observed in VSe 2 and TiTe 2 . Interference effects together with a non-free-electron nature of final states strongly limit the applicability of the common direct transitions band mapping approach, making the tool of one-step analysis indispensable.
Journal of Electron Spectroscopy and Related Phenomena, 2001
We have studied by high resolution ARPES the spectroscopic properties of the prototype charge den... more We have studied by high resolution ARPES the spectroscopic properties of the prototype charge density wave system (TaSe ) I and of the closely related insulating compound (NbSe ) I. We observe features dispersing with the lattice 4 2 4 3 periodicity, including commensurate (in (NbSe ) I) and incommensurate (in (TaSe ) I) superlattice shadow bands. The 4 3 4 2
Japanese Journal of Applied Physics, 1999
Optical, X-ray and DSC measurements on N(CH 3 ) 4 HSO 4
Ferroelectrics, 1990
X-ray diffraction measurements on single crystals of N(CH3)HSO have shown the following sequence ... more X-ray diffraction measurements on single crystals of N(CH3)HSO have shown the following sequence of phases: Orthorhombic, Normal ⌆ Ti = 235K ⌆ Orthorhombic, Incommensurate ⌆ Tc = 202K ⌆ Monoclinic, Commensurate. DSC and birefringence measurements show a second order phase transition at Ti and a first order one at Tc.
Piezoelectric properties of quasi one-dimensional conductor (TaSe 4 ) 2 I
Le Journal de Physique IV, 1999
ABSTRACT Frequency dependence of the electrical impedance of (TaSe4)(2)I crystals was studied bet... more ABSTRACT Frequency dependence of the electrical impedance of (TaSe4)(2)I crystals was studied between 4.2-150K in the frequency range 0.1-20MHz. In all experiments the voltage was applied (and measured) perpendicular to the c axis. We observed a resonance the frequency of which was inversely proportional to the dimension of the sample in the direction of mechanical oscillations, in agreement with the theory of piezoelectric effect. An additional confirmation of the piezoelectric origin of the resonance was found by the excitation of ultrasound waves at 77K in (TaSe4)(2)I by the intrinsic piezoeffect. We verified that velocity of sound propagation through the sample in both types of experiments was equal to the velocity of C-44 sound wave.
Physical Review B, 2006
Three-dimensional band structure of unoccupied and occupied states of the prototype layered mater... more Three-dimensional band structure of unoccupied and occupied states of the prototype layered material TiTe 2 is determined focusing on the ΓA line of the Brillouin zone. Dispersions and lifetimes of the unoccupied states, acting as the final states in the photoemission process, are determined from a very-low-energy electron diffraction experiment supported by first-principles calculations based on a Bloch waves treatment of multiple scattering. The experimental unoccupied states of TiTe 2 feature dramatic non-free-electron effects such as multiband composition and non-parabolic dispersions. The valence band layer-perpendicular dispersions are then determined from a photoemission experiment consistently interpreted on the basis of the experimental final states to achieve control over the 3-dimensional wavevector. The experimental results demonstrate the absence of the Te 4p z * Fermi surface pocket at the Γ point and significant self-energy renormalization of the valence band dispersions. Photoemission calculations based on a novel Bloch waves formalism within the one-step theory reveal limitations of understanding photoemission from layered materials such as TiTe 2 in terms of direct transitions.
Multiferroicity in the geometrically frustrated FeTe2O5Cl
Physical Review B, 2013
Magnetic order and low-energy excitations in the quasi-one-dimensional antiferromagnet CuSe2O5 with staggered fields
Physical Review B, 2013
Physical Review B, 2008
We present new muon spectroscopy data on a Fe3O4 single crystal, revealing different spin precess... more We present new muon spectroscopy data on a Fe3O4 single crystal, revealing different spin precession patterns in five distinct temperature ranges. A careful analysis of the local field and its straightforward modeling obtains surprisingly good agreement with experiments only if a very specific model of localized charges violating Anderson condition, and a correlated muon local dynamics are implemented. Muon evidence for fluctuations just above the Verwey temperature, precursor of the low temperature charge localized state, is provided.
Journal of Physics: Condensed Matter, 2007
The crystal structure of a new modification of NiSeO 3 is described together with its magnetic pr... more The crystal structure of a new modification of NiSeO 3 is described together with its magnetic properties. The new polymorph crystallizes in the monoclinic system, space group C2/c, with unit cell parameters a = 15.4965(7)Å, b = 9.8250(4)Å, c = 14.7278(8)Å, β = 110.610(4) • and Z = 8. The crystal structure was solved from single crystal data, R = 0.0252. The structure can be considered as being layered along the bc-plane with [NiO 6 ] octahedra arranged into two sub-groups. The layers are further connected to adjacent layers via groups of two edge-sharing [NiO 6 ] octahedra. The Ni octahedra are tilted and are either edge or corner sharing, giving rise to two different Ni-Ni interactions. The lone pairs of Se 4+ occupy non-bonding regions of tunnels along [001] and [010]. The complexity of the crystal structure is also reflected in the complex low-temperature magnetic state. An antiferromagnetic-like transition was observed at T tr = 14.4 K. A possible structural rearrangement closely above T tr complicates the details of the lowtemperature state. The antiferromagnetic-like transition disagrees with the features of a three-dimensional (3D) Néel antiferromagnetic ordering. This is mostly because of the fact that the assumed bulk easy-axis susceptibility at the lowest temperature remains at high paramagnetic value. The consequences of the complex structure on basic magnetic parameters, zero-field splitting energy D and exchange coupling J , and accordingly on the magnetic properties, are discussed.
Strong electron interactions in solids increase effective mass, and shrink the electronic bands [... more Strong electron interactions in solids increase effective mass, and shrink the electronic bands [1]. One of the most unique and robust experimental facts about iron-based superconductors is the renormalization of the conduction band by factor of 3 near the Fermi level . Obviously related to superconductivity, this unusual behaviour remains unexplained. Here, by studying the momentum-resolved spectrum of the whole valence band in a representative material, we show that this phenomenon originates from electronic interaction on a much larger energy scale. We observe an abrupt depletion of the spectral weight in the middle of the Fe 3d band, which is accompanied by a drastic increase of the scattering rate. Remarkably, all spectral anomalies including the low-energy renormalization can be explained by coupling to excitations, strongly peaked at about 0.5 eV. Such high-energy interaction distinguishes all unconventional superconductors from common metals.
Review of Scientific Instruments
Time-and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast ele... more Time-and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Timeand angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup. ©2014AIPPublishingLLC.[http://dx.doi.org/10.1063/1.4903347]
Physical Review Letters, 2014
Uniquely in Cu 2 OSeO 3 , the Skyrmions, which are topologically protected magnetic spin vortexli... more Uniquely in Cu 2 OSeO 3 , the Skyrmions, which are topologically protected magnetic spin vortexlike objects, display a magnetoelectric coupling and can be manipulated by externally applied electric (E) fields. Here, we explore the E-field coupling to the magnetoelectric Skyrmion lattice phase, and study the response using neutron scattering. Giant E-field induced rotations of the Skyrmion lattice are achieved that span a range of ∼25°. Supporting calculations show that an E-field-induced Skyrmion distortion lies behind the lattice rotation. Overall, we present a new approach to Skyrmion control that makes no use of spin-transfer torques due to currents of either electrons or magnons.
The Journal of Physical Chemistry C
We report resistivity, thermoelectric power, and thermal conductivity of MoS 2 single crystals pr... more We report resistivity, thermoelectric power, and thermal conductivity of MoS 2 single crystals prepared by the chemical vapor transport (CVT) method using I 2 , Br 2 , and TeCl 4 as transport agents. The material presents low-lying donor and acceptor levels, which dominate the in-plane charge transport. Intercalates into the van der Waals gap strongly influence the interplane resistivity. Thermoelectric power displays the characteristics of strong electron−phonon interaction. A detailed theoretical model of thermal conductivity reveals the presence of a high number of defects in the MoS 2 structure. We show that these defects are inherent to CVT growth method, coming mostly from the transport agent molecules inclusion as identified by total reflection X-ray fluorescence analysis (TXRF) and in-beam activation analysis (IBAA).
Physical Review B, 2014
Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spi... more Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spintronics devices because of the coexistence of spin-split bulk and surface states, along with the ambipolar character of the surface charge carriers. The need to study the spin texture of strongly spin-orbit-coupled materials has recently promoted circular dichroic angular resolved photoelectron spectroscopy (CD-ARPES) as an indirect tool to measure the spin and the angular degrees of freedom. Here we report a detailed photon-energy-dependent study of the CD-ARPES spectra in BiTeX (X = I, Br, Cl). Our work reveals a large variation in the magnitude and sign of the dichroism. Interestingly, we find that the dichroic signal modulates differently for the three compounds and for the different spin-split states. These findings show a momentum and photon-energy dependence for the CD-ARPES signals in the bulk Rashba semiconductor BiTeX (X = I, Br, Cl). Finally, the outcome of our experiment indicates the important relation between the modulation of the dichroism and the phase differences between the wave functions involved in the photoemission process. This phase difference can be due to initialor final-state effects. In the former case the phase difference results in possible interference effects among the photoelectrons emitted from different atomic layers and characterized by entangled spin-orbital polarized bands. In the latter case the phase difference results from the relative phases of the expansion of the final state in different outgoing partial waves.
Low Temperature Physics, 2008
The magnetic and magnetoresonance properties of a new single-crystal compound Ni 5 ͑TeO 3 ͒ 4 Cl ... more The magnetic and magnetoresonance properties of a new single-crystal compound Ni 5 ͑TeO 3 ͒ 4 Cl 2 are studied. Measurements of the magnetization and magnetic susceptibility of the crystal in a wide temperature range ͑5 -300 K͒ make it possible to conclude that Ni 5 ͑TeO 3 ͒ 4 Cl 2 is a quasitwo-dimensional antiferromagnet with the easy magnetization axis a * directed perpendicular to the crystallographic plane bc and a magnetic ordering temperature T N Ϸ 21 K. Resonance measurements at 4.2 K in wide range of frequencies ͑25-105 GHz͒ and magnetic field ͑up to 200 kOe͒ permit us to obtain the frequency-field dependence of the AFMR spectrum for a field applied along the easy magnetization axis a * . It is shown that a magnetic field directed along the antiferromagnetic axis ͑H ʈ a * ͒ induces a magnetic phase transition of the spin-flop type, which is found to occur at H sf Ϸ 120 kOe. The magnetic resonance experimental data are described qualitatively in the model of a biaxial antiferromagnet.
Spectroscopic signature of magnetic exchange with high resolution RIXS
New Journal of Physics, 2008
By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the... more By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the fermiology of 2H transition metal dichalcogenide polytypes TaSe 2 , NbSe 2 , and Cu 0.2 NbS 2 . The tightbinding model of the electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate the Lindhard function (bare spin susceptibility), which reflects the propensity to charge density wave (CDW) instabilities observed in TaSe 2 and NbSe 2 . We show that though the Fermi surfaces of all three compounds possess an incommensurate nesting vector in the close vicinity of the CDW wave vector, the nesting and ordering wave vectors do not exactly coincide, and there is no direct relationship between the magnitude of the susceptibility at the nesting vector and the CDW transition temperature. The nesting vector persists across the incommensurate CDW transition in TaSe 2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu 0.2 NbS 2 the nesting vector is present despite different doping level, which lets us expect a possible enhancement of the CDW instability with Cu-intercalation in the Cu x NbS 2 family of materials. PACS numbers: 71.45.Lr 79.60.-i 71.18.+y 74.25.Jb
Physica C: Superconductivity, 2007
The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects... more The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects in angle resolved photoelectron spectra (ARPES) of Bi 2 Sr 2 CaCu 2 O 8+d is addressed. We show that the nonmagnetic Zn atoms have much stronger effect both in nodal and antinodal parts of the Brillouin zone than magnetic Ni. The observed changes are consistent with the behaviour of the spin resonance mode as seen by inelastic neutron scattering in YBCO-123. This strongly suggests that the ''peak-dip-hump'' and the ''kink'' in ARPES on the one side and neutron resonance on the other are closely related features.
Physical Review B, 2007
A novel Bloch-waves based one-step theory of photoemission is developed within the augmented plan... more A novel Bloch-waves based one-step theory of photoemission is developed within the augmented plane wave formalism. Implications of multi-Bloch-wave structure of photoelectron final states for band mapping are established. Interference between Bloch components of initial and final states leads to prominent spectral features with characteristic frequency dispersion experimentally observed in VSe 2 and TiTe 2 . Interference effects together with a non-free-electron nature of final states strongly limit the applicability of the common direct transitions band mapping approach, making the tool of one-step analysis indispensable.
Journal of Electron Spectroscopy and Related Phenomena, 2001
We have studied by high resolution ARPES the spectroscopic properties of the prototype charge den... more We have studied by high resolution ARPES the spectroscopic properties of the prototype charge density wave system (TaSe ) I and of the closely related insulating compound (NbSe ) I. We observe features dispersing with the lattice 4 2 4 3 periodicity, including commensurate (in (NbSe ) I) and incommensurate (in (TaSe ) I) superlattice shadow bands. The 4 3 4 2
Japanese Journal of Applied Physics, 1999
Optical, X-ray and DSC measurements on N(CH 3 ) 4 HSO 4
Ferroelectrics, 1990
X-ray diffraction measurements on single crystals of N(CH3)HSO have shown the following sequence ... more X-ray diffraction measurements on single crystals of N(CH3)HSO have shown the following sequence of phases: Orthorhombic, Normal ⌆ Ti = 235K ⌆ Orthorhombic, Incommensurate ⌆ Tc = 202K ⌆ Monoclinic, Commensurate. DSC and birefringence measurements show a second order phase transition at Ti and a first order one at Tc.
Piezoelectric properties of quasi one-dimensional conductor (TaSe 4 ) 2 I
Le Journal de Physique IV, 1999
ABSTRACT Frequency dependence of the electrical impedance of (TaSe4)(2)I crystals was studied bet... more ABSTRACT Frequency dependence of the electrical impedance of (TaSe4)(2)I crystals was studied between 4.2-150K in the frequency range 0.1-20MHz. In all experiments the voltage was applied (and measured) perpendicular to the c axis. We observed a resonance the frequency of which was inversely proportional to the dimension of the sample in the direction of mechanical oscillations, in agreement with the theory of piezoelectric effect. An additional confirmation of the piezoelectric origin of the resonance was found by the excitation of ultrasound waves at 77K in (TaSe4)(2)I by the intrinsic piezoeffect. We verified that velocity of sound propagation through the sample in both types of experiments was equal to the velocity of C-44 sound wave.
Physical Review B, 2006
Three-dimensional band structure of unoccupied and occupied states of the prototype layered mater... more Three-dimensional band structure of unoccupied and occupied states of the prototype layered material TiTe 2 is determined focusing on the ΓA line of the Brillouin zone. Dispersions and lifetimes of the unoccupied states, acting as the final states in the photoemission process, are determined from a very-low-energy electron diffraction experiment supported by first-principles calculations based on a Bloch waves treatment of multiple scattering. The experimental unoccupied states of TiTe 2 feature dramatic non-free-electron effects such as multiband composition and non-parabolic dispersions. The valence band layer-perpendicular dispersions are then determined from a photoemission experiment consistently interpreted on the basis of the experimental final states to achieve control over the 3-dimensional wavevector. The experimental results demonstrate the absence of the Te 4p z * Fermi surface pocket at the Γ point and significant self-energy renormalization of the valence band dispersions. Photoemission calculations based on a novel Bloch waves formalism within the one-step theory reveal limitations of understanding photoemission from layered materials such as TiTe 2 in terms of direct transitions.
Multiferroicity in the geometrically frustrated FeTe2O5Cl
Physical Review B, 2013
Magnetic order and low-energy excitations in the quasi-one-dimensional antiferromagnet CuSe2O5 with staggered fields
Physical Review B, 2013
Physical Review B, 2008
We present new muon spectroscopy data on a Fe3O4 single crystal, revealing different spin precess... more We present new muon spectroscopy data on a Fe3O4 single crystal, revealing different spin precession patterns in five distinct temperature ranges. A careful analysis of the local field and its straightforward modeling obtains surprisingly good agreement with experiments only if a very specific model of localized charges violating Anderson condition, and a correlated muon local dynamics are implemented. Muon evidence for fluctuations just above the Verwey temperature, precursor of the low temperature charge localized state, is provided.
Journal of Physics: Condensed Matter, 2007
The crystal structure of a new modification of NiSeO 3 is described together with its magnetic pr... more The crystal structure of a new modification of NiSeO 3 is described together with its magnetic properties. The new polymorph crystallizes in the monoclinic system, space group C2/c, with unit cell parameters a = 15.4965(7)Å, b = 9.8250(4)Å, c = 14.7278(8)Å, β = 110.610(4) • and Z = 8. The crystal structure was solved from single crystal data, R = 0.0252. The structure can be considered as being layered along the bc-plane with [NiO 6 ] octahedra arranged into two sub-groups. The layers are further connected to adjacent layers via groups of two edge-sharing [NiO 6 ] octahedra. The Ni octahedra are tilted and are either edge or corner sharing, giving rise to two different Ni-Ni interactions. The lone pairs of Se 4+ occupy non-bonding regions of tunnels along [001] and [010]. The complexity of the crystal structure is also reflected in the complex low-temperature magnetic state. An antiferromagnetic-like transition was observed at T tr = 14.4 K. A possible structural rearrangement closely above T tr complicates the details of the lowtemperature state. The antiferromagnetic-like transition disagrees with the features of a three-dimensional (3D) Néel antiferromagnetic ordering. This is mostly because of the fact that the assumed bulk easy-axis susceptibility at the lowest temperature remains at high paramagnetic value. The consequences of the complex structure on basic magnetic parameters, zero-field splitting energy D and exchange coupling J , and accordingly on the magnetic properties, are discussed.
Strong electron interactions in solids increase effective mass, and shrink the electronic bands [... more Strong electron interactions in solids increase effective mass, and shrink the electronic bands [1]. One of the most unique and robust experimental facts about iron-based superconductors is the renormalization of the conduction band by factor of 3 near the Fermi level . Obviously related to superconductivity, this unusual behaviour remains unexplained. Here, by studying the momentum-resolved spectrum of the whole valence band in a representative material, we show that this phenomenon originates from electronic interaction on a much larger energy scale. We observe an abrupt depletion of the spectral weight in the middle of the Fe 3d band, which is accompanied by a drastic increase of the scattering rate. Remarkably, all spectral anomalies including the low-energy renormalization can be explained by coupling to excitations, strongly peaked at about 0.5 eV. Such high-energy interaction distinguishes all unconventional superconductors from common metals.
Review of Scientific Instruments
Time-and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast ele... more Time-and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Timeand angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup. ©2014AIPPublishingLLC.[http://dx.doi.org/10.1063/1.4903347]
Physical Review Letters, 2014
Uniquely in Cu 2 OSeO 3 , the Skyrmions, which are topologically protected magnetic spin vortexli... more Uniquely in Cu 2 OSeO 3 , the Skyrmions, which are topologically protected magnetic spin vortexlike objects, display a magnetoelectric coupling and can be manipulated by externally applied electric (E) fields. Here, we explore the E-field coupling to the magnetoelectric Skyrmion lattice phase, and study the response using neutron scattering. Giant E-field induced rotations of the Skyrmion lattice are achieved that span a range of ∼25°. Supporting calculations show that an E-field-induced Skyrmion distortion lies behind the lattice rotation. Overall, we present a new approach to Skyrmion control that makes no use of spin-transfer torques due to currents of either electrons or magnons.
The Journal of Physical Chemistry C
We report resistivity, thermoelectric power, and thermal conductivity of MoS 2 single crystals pr... more We report resistivity, thermoelectric power, and thermal conductivity of MoS 2 single crystals prepared by the chemical vapor transport (CVT) method using I 2 , Br 2 , and TeCl 4 as transport agents. The material presents low-lying donor and acceptor levels, which dominate the in-plane charge transport. Intercalates into the van der Waals gap strongly influence the interplane resistivity. Thermoelectric power displays the characteristics of strong electron−phonon interaction. A detailed theoretical model of thermal conductivity reveals the presence of a high number of defects in the MoS 2 structure. We show that these defects are inherent to CVT growth method, coming mostly from the transport agent molecules inclusion as identified by total reflection X-ray fluorescence analysis (TXRF) and in-beam activation analysis (IBAA).
Physical Review B, 2014
Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spi... more Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spintronics devices because of the coexistence of spin-split bulk and surface states, along with the ambipolar character of the surface charge carriers. The need to study the spin texture of strongly spin-orbit-coupled materials has recently promoted circular dichroic angular resolved photoelectron spectroscopy (CD-ARPES) as an indirect tool to measure the spin and the angular degrees of freedom. Here we report a detailed photon-energy-dependent study of the CD-ARPES spectra in BiTeX (X = I, Br, Cl). Our work reveals a large variation in the magnitude and sign of the dichroism. Interestingly, we find that the dichroic signal modulates differently for the three compounds and for the different spin-split states. These findings show a momentum and photon-energy dependence for the CD-ARPES signals in the bulk Rashba semiconductor BiTeX (X = I, Br, Cl). Finally, the outcome of our experiment indicates the important relation between the modulation of the dichroism and the phase differences between the wave functions involved in the photoemission process. This phase difference can be due to initialor final-state effects. In the former case the phase difference results in possible interference effects among the photoelectrons emitted from different atomic layers and characterized by entangled spin-orbital polarized bands. In the latter case the phase difference results from the relative phases of the expansion of the final state in different outgoing partial waves.