Evidence for coupling between charge-density-wave and phonons in two-dimensional rare-earth tri-tellurides (original) (raw)

2009

https://doi.org/10.1103/PHYSREVB.78.201101

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Abstract

We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi two-dimensional rare-earth tri-tellurides RTe3 (R= La, Ce, Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe3 and CeTe3 under externally applied pressure. The observed phonon peaks can be ascribed to the Raman active modes for both the undistorted as well as the distorted lattice in

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Physical Review B, 2008

The charge density wave transition is investigated in the bi-layer family of rare earth tritelluride RTe3 compounds (R = Sm, Gd, Tb, Dy, Ho, Er, Tm) via high resolution x-ray diffraction and electrical resistivity. The transition temperature increases monotonically with increasing lattice parameter from 244(3) K for TmTe3 to 416(3) K for SmTe3. The heaviest members of the series, R = Dy, Ho, Er, Tm, are observed to have a second transition at a lower temperature, which marks the onset of an additional CDW with wavevector almost equal in magnitude to the first, but oriented in the perpendicular direction.

Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tritellurides

Physical Review B

We performed resonant soft X-ray diffraction on known charge density wave (CDW) compounds, rare earth tri-tellurides. Near the M5 (3d -4f ) absorption edge of rare earth ions, an intense diffraction peak is detected at a wavevector identical to that of CDW state hosted on Te2 planes, indicating a CDW-induced modulation on the rare earth ions. Surprisingly, the temperature dependence of the diffraction peak intensity demonstrates an exponential increase at low temperatures, vastly different than that of the CDW order parameter. Assuming 4f multiplet splitting due to the CDW states,we present a model to calculate X-ray absorption spectrum and resonant profile of the diffraction peak, agreeing well with experimental observations. Our results demonstrate a situation where the temperature dependence of resonant X-ray diffraction peak intensity is not directly related to the intrinsic behavior of the order parameter associated with the electronic order, but is dominated by the thermal occupancy of the valence states.

Theory of stripes in quasi-two-dimensional rare-earth tellurides

Physical Review B, 2006

Even though the rare-earth tritellurides are tetragonal materials with a quasi two dimensional (2D) band structure, they have a "hidden" 1D character. The resultant near-perfect nesting of the Fermi surface leads to the formation of a charge density wave (CDW) state. We show that for this band structure, there are two possible ordered phases: A bidirectional "checkerboard" state would occur if the CDW transition temperature were sufficiently low, whereas a unidirectional "striped" state, consistent with what is observed in experiment, is favored when the transition temperature is higher. This result may also give some insight into why, in more strongly correlated systems, such as the cuprates and nickelates, the observed charge ordered states are generally stripes as opposed to checkerboards.

Fermi surface nesting and charge-density wave formation in rare-earth tritellurides

Physical Review B, 2005

The Fermi surface of rare-earth tri-tellurides (RTe3) is investigated in terms of the nesting driven charge-density wave formation using positron annihilation and first-principles LMTO calculations. Fermi surface nesting is revealed as a strong candidate for driving charge-density wave formation in these compounds. The nesting vector obtained from positron annihilation experiments on GdTe3 is determined to be q = (0.28 ± 0.02, 0, 0) a * , (a * = 2π/a), in excellent agreement with previous experimental and theoretical studies.

Charge density wave formation in R2Te5 (R=Nd, Sm, and Gd)

Physical Review B, 2008

The rare earth (R) tellurides R2Te5 have a crystal structure intermediate between that of RTe2 and RTe3, consisting of alternating single and double Te planes sandwiched between RTe block layers. We have successfully grown single crystals of Nd2Te5, Sm2Te5 and Gd2Te5 from a self flux, and describe here the first evidence for charge density wave formation in these materials. The superlattice patterns for all three compounds are relatively complex, consisting at room temperature of at least two independent wavevectors. Consideration of the electronic structure indicates that to a large extent these wave vectors are separately associated with sheets of the Fermi surface which are principally derived from the single and double Te layers.

Linear magnetoresistance in the charge density wave state of quasi-two-dimensional rare-earth tritellurides

Physical Review B, 2017

We report measurements of the magnetoresistance in the charge density wave (CDW) state of rare-earth tritellurides, namely TbTe3 and HoTe3. The magnetic field dependence of magnetoresistance exhibits a temperature dependent crossover between a conventional quadratic law at high T and low B and an unusual linear dependence at low T and high B. We present a quite general model to explain the linear magnetoresistance taking into account the strong scattering of quasiparticles on CDW fluctuations in the vicinity of "hot spots" of the Fermi surface (FS) where the FS reconstruction is the strongest.

Interplay of charge density wave states and strain at the surface of CeTe2

Physical Review B

We use scanning tunneling microscopy (STM) to study charge density wave (CDW) states in the rare-earth ditelluride, CeTe 2. Our STM measurements surprisingly detect a unidirectional CDW with q ∼ 0.28 a * , which differs from previous experimental and first-principles studies of the rare-earth ditellurides, and which is very close to what is found in experimental measurements of the related rare-earth tritellurides. Furthermore, in the vicinity of an extended subsurface defect, we find spatially-separated as well as spatially-coexisting unidirectional CDWs at the surface of CeTe 2. We quantify the nanoscale strain and its variations induced by this defect, and establish a correlation between local lattice strain and the locally-established CDW states; this suggests that lattice strain plays an important role in determining the specific characteristics of the established CDW state. Our measurements probe the fundamental properties of a weakly-bound two-dimensional Te sheet, which experimental and theoretical work has previously established as the fundamental component driving much of the essential physics in both the rare-earth di-and tritelluride compounds.

Phonon and crystal field excitations in geometrically frustrated rare earth titanates

Physical Review B, 2008

The phonon and crystal field excitations in several rare earth titanate pyrochlores are investigated. Magnetic measurements on single crystals of Gd2Ti2O7, Tb2Ti2O7, Dy2Ti2O7 and Ho2Ti2O7 are used for characterization, while Raman spectroscopy and terahertz time domain spectroscopy are employed to probe the excitations of the materials. The lattice excitations are found to be analogous across the compounds over the whole temperature range investigated (295-4 K). The resulting full phononic characterization of the R2Ti2O7 pyrochlore structure is then used to identify crystal field excitations observed in the materials. Several crystal field excitations have been observed in Tb2Ti2O7 in Raman spectroscopy for the first time, among which all of the previously reported excitations. The presence of additional crystal field excitations, however, suggests the presence of two inequivalent Tb 3+ sites in the low temperature structure. Furthermore, the crystal field level at approximately 13 cm −1 is found to be both Raman and dipole active, indicating broken inversion symmetry in the system and thus undermining its current symmetry interpretation. In addition, evidence is found for a significant crystal field-phonon coupling in Tb2Ti2O7. These findings call for a careful reassessment of the low temperature structure of Tb2Ti2O7, which may serve to improve its theoretical understanding.

Generalized electronic susceptibility and charge-density waves in 2H-TaSe2by Raman scattering

Physical Review B, 1982

The lattice vibration in 28-TaSe2 was investigated by oneand two-phonon Raman scattering in the normal and the charge-density-wave I'CD%) phases. From the integrated scattering intensity of the two-phonon-process peak, the temperature dependence of the generalized electronic susceptibility was obtained, 3nd with its use the temperature dependence of the phonon energies was calculated. Agreement with the experimentally obtained temperature dependence of phonon energies is excellent in the soft 3~g and E2g modes in the CD% phase and the Kohn-anomaly mode in the normal phase, which was obtained from the lower-energy base of the two-phonon-process peak. No hysteresis was observed in the Raman spectra at the temperature region of the single commensurate phase on warming and cooling. The spectra change smoothly and continuously over the three CD% phases. These suggest the existence of the domain structure where the CD% is nearly commensurate in the domain. I. INTRODUCTION Low-dimensional materials aroose much interest due to their unique properties. One such property is a charge-density-wave (CDW) state which comes from the special properties of low-dimensional electronic band structures, electron-electron interactions, and electron-lattice interactions. The CD% state has lower energy than the original structure, only accompanied by lattice distortion, in contrast with a spin-density-wave state which can be realized without lattice distortion. The CD% states are known in one-dimensional organic and inorganic materials, and two-dimensional tfRnsitlon-IDctR1 dlchRlcogcnldcs. MctRlllc coIn™ pounds of sulfides and selenides of group-VB elements (Ta, V, and Nb) show the CDW phase transition' ' and a sernirnetallic compound of a group-IVB element (TlSe2) shows a comparable phase transition. These compounds have polymorphic structures and each shows a specific phase transition. The basic structures of the polymorphism are 1T and 2H structures. The CD%' states in 2II-TaSC2 have been best studied by neutron, ' x-ray, " and electron diffraction' to determine the crystal structure, by neutron ' Raman scRttcI'lng to dctcfminc thc 1Rttlcc vibration, by electric transport ' ' de Haasvan Alphen Shubnikovde Ha3s oscillation, specificheat, ' ' ultrasonic angle-resolved ultraviolet photoemission, infrared reAection, ' thermal expansion, and NMR measurements. ' %exler and %ooley have calculated the band structure and Wilson, ' McMlllan, and Nakanlshl and

Pressure-Induced Phase Transitions in Germanium Telluride: Raman Signatures of Anharmonicity and Oxidation

Physical Review Letters, 2019

Pressure induced phase transitions in GeTe, a prototype phase change material have been studied to date with diffraction which is not sensitive to anharmonicity induced dynamical effects. GeTe is also prone to surface oxidation which may compromise surface sensitive measurements. These factors could be responsible for the lack of clarity about the phases and transitions intervening in the phase diagram of GeTe. We have used high pressure Raman scattering and ab initio pseudopotential density functional calculations to unambiguously establish the high pressure phase diagram and identify three phases up to 57 GPa, a low-pressure rhombohedral phase, an intermediate pressure cubic phase and a high pressure orthorhombic phase. We detect substantial broadening and softening of Raman modes at low pressure and identify the transition regions and possible intermediate phases.

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References (27)

͑2008͒.
G. Grüner, Density Waves in Solids ͑Addison-Wesley, Reading, MA, 1994͒.
J. A. Wilson, F. J. DiSalvo, and S. Mahajan, Adv. Phys. 24, 117 ͑1975͒.
J. Rouxel, in Crystal Chemistry and Properties of Materials with Quasi-One-Dimensional Structures, edited by J. Rouxel and D. Reidel ͑Springer, Dordrecht, 1986͒, pp. 1-26.
T. Vuletić, B. Korin-Hamzić, T. Ivek, S. Tomić, B. Gorshunov, M. Dressel, and J. Akimitsu, Phys. Rep. 428, 169 ͑2006͒.
See Sec. V of S. A. Kivelson, I. P. Bindloss, E. Fradkin, V. Oganesyan, J. M. Tranquada, A. Kapitulnik, and C. Howald, Rev. Mod. Phys. 75, 1201 ͑2003͒.
H. Yao, J. A. Robertson, E. A. Kim, and S. A. Kivelson, Phys. Rev. B 74, 245126 ͑2006͒.
E. DiMasi, M. C. Aronson, J. F. Mansfield, B. Foran, and S. Lee, Phys. Rev. B 52, 14516 ͑1995͒.
N. Ru and I. R. Fisher, Phys. Rev. B 73, 033101 ͑2006͒.
N. Ru, C. L. Condron, G. Y. Margulis, K. Y. Shin, J. Laverock, S. B. Dugdale, M. F. Toney, and I. R. Fisher, Phys. Rev. B 77, 035114 ͑2008͒.
A. Sacchetti, L. Degiorgi, T. Giamarchi, N. Ru, and I. R. Fisher, Phys. Rev. B 74, 125115 ͑2006͒.
A. Sacchetti, E. Arcangeletti, A. Perucchi, L. Baldassarre, P. Pos- torino, S. Lupi, N. Ru, I. R. Fisher, and L. Degiorgi, Phys. Rev. Lett. 98, 026401 ͑2007͒.
V. Brouet, W. L. Yang, X. J. Zhou, Z. Hussain, N. Ru, K. Y. Shin, I. R. Fisher, and Z. X. Shen, Phys. Rev. Lett. 93, 126405 ͑2004͒.
As the temperature dependence of the CDW gap is not known in RTe 3 , we choose pressure ͑both chemical and applied͒ as tun- able variable.
G. J. Piermarini, S. Block, and J. D. Barnett, J. Appl. Phys. 44, 5377 ͑1973͒.
H. K. Mao, J. Xu, and P. M. Bell, J. Geophys. Res. 91, 4673 ͑1986͒.
B. K. Norling and H. Steinfink, Inorg. Chem. 5, 1488 ͑1966͒.
W. G. Fately, F. R. Dollish, N. T. McDevitt, and F. F. Bentley, Infrared and Raman Selection Rules for Molecular and Lattice Vibrations: The Correlation Method ͑Wiley, New York, 1972͒. 20 The calculations were done with hardness-conserving semilocal pseudopotentials for all states below the 4d shell for Te and the 5s shell for the rare-earth atoms ͓B. Delley, Phys. Rev. B 66, 155125 ͑2002͔͒, and used the DNP basis set ͓B. Delley, J. Chem. Phys. 92, 508 ͑1990͒; 113, 7756 ͑2000͔͒; the k-space integrations have been performed with an unshifted 6 ϫ 2 ϫ 6 ͑2 ϫ 2 ϫ 6͒ mesh, which amounts to 40 ͑16͒ symmetry unique k points in the calculations for the primitive ͑super͒cell. A thermal broadening of 1 mHartree has been used. The total energy has been modified with the entropy term proposed by M. Weinert and J. W. Davenport, Phys. Rev. B 45, 13709 ͑1992͒ to make the energy functional variational.
An orthorhombic pseudotetragonal ͑a = c͒ structure was consid- ered, as the small deviations between a and c were found to be insignificant in an earlier high-precision calculation of the Fermi surface ͓J. Laverock, S. B. Dugdale, Z. Major, M. A. Alam, N. Ru, I. R. Fisher, G. Santi, and E. Bruno, Phys. Rev. B 71, 085114 ͑2005͔͒.
P. Villars and L. D. Calvert, Pearsons Handbook of Crystallo- graphic Data for Intermetallic Phases ͑American Society for Metals, Metals Park, OH, 1991͒.
We also collected data ͑not shown here͒ with the scattered light polarization orthogonal to the incident one and obtained results fully consistent with those of the parallel polarization ͓Fig. 3͑a͔͒.
C. Malliakas, S. J. L. Billinge, H. J. Kim, and M. G. Kanatzidis, J. Am. Chem. Soc. 127, 6510 ͑2005͒.
The unit cell in the distorted structure is not centrosymmetric anymore, so that the A 1g symmetry turns into A 1 . The period of the angle-dependent intensity is 180°͑90°͒ for the A 1 ͑B 1 ͒ sym- metry.
26 The sudden disappearance of the modes in the Raman spectra of Gd and Dy tritellurides ͓Fig. 1͑a͔͒ could also originate from the fact that the data were collected at 300 K, i.e., just slightly below their own T CDW ͑Ref. 11͒.
27 The behavior of the weak P3 and P5 peaks is less well defined, while the intensity of the P1 peak, which is only partially seen in the chemical-pressure series, does not seem to change much.
M. J. Rice, Phys. Rev. Lett. 37, 36 ͑1976͒; Solid State Commun. 25, 1083 ͑1978͒.
J. Petzelt and V. Dvořák, J. Phys. C 9, 1571 ͑1976͒.

Evidence for coupling between collective state and phonons in two-dimensional charge-density-wave systems

2008

We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi twodimensional rare-earth tri-tellurides RTe 3 (R= La, Ce, Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe 3 and CeTe 3 under externally applied pressure. The observed phonon peaks can be ascribed to the Raman active modes for both the undistorted as well as the distorted lattice in the CDW state by means of a first principles calculation. The latter also predicts the Kohn anomaly in the phonon dispersion, driving the CDW transition. The integrated intensity of the two most prominent modes scales as a characteristic power of the CDW-gap amplitude upon compressing the lattice, which provides clear evidence for the tight coupling between the CDW condensate and the vibrational modes.

Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tritellurides

Physical Review Letters, 2007

We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3.

Effect of chemical pressure on the charge density wave transition in rare-earth tritellurides RTe3

Physical Review B, 2008

Charge transfer and multiple density waves in the rare earth tellurides

Physical Review B, 2013

We use high-resolution synchrotron x-ray diffraction to uncover a second, low-temperature, charge density wave (CDW) in TbTe 3 . Its T c 2 = 41.0 ± 0.4 K is the lowest discovered so far in the rare earth telluride series. The CDW wave vectors of the high temperature and low temperature states differ significantly and evolve in opposite directions with temperature, indicating that the two nested Fermi surfaces are separated and the CDWs coexist independently. Both the in-plane and out-of-plane correlation lengths are robust, implying that the density waves on different Te layers are well coupled through the TbTe layers. Finally, we rule out any low-temperature CDW in GdTe 3 for temperatures above 8 K, an energy scale sufficiently low to make pressure tuning of incipient CDW order a realistic possibility.

Pressure-induced quenching of the charge-density-wave state in rare-earth tritellurides observed by x-ray diffraction

Physical Review B, 2009

We report an x-ray diffraction study on the charge-density-wave ͑CDW͒ LaTe 3 and CeTe 3 compounds as a function of pressure. We extract the lattice constants and the CDW modulation wave vector. We observe that the intensity of the CDW satellite peaks tend to zero with increasing pressure, thus providing direct evidence for a pressure-induced quenching of the CDW phase. Our findings further support the equivalence between chemical and applied pressures in RTe 3 , put forward by our previous optical investigations, but reveal some subtle differences. We offer a possible explanation for these differences.

Phonon origin and lattice evolution in charge density wave states

Physical Review B, 2019

Metallic transition metal dichalcogenides, such as tantalum diselenide (TaSe 2), display quantum correlated phenomena of superconductivity and charge density waves (CDW) at low temperatures. Here, the photophysics of 2H-TaSe 2 during CDW transitions is revealed by combining temperature-dependent, low-frequency Raman spectroscopy and density functional theory (DFT). The spectra contain amplitude, phase, and zone-folded modes that are assigned to specific phonons and lattice restructuring predicted by DFT calculations with superb agreement. The non-invasive and efficient optical methodology detailed here demonstrates an essential link between atomic-scale and microscopic quantum phenomena.

Pressure dependence of Raman modes in double wall carbon nanotubes lled with 1D tellurium

HAL (Le Centre pour la Communication Scientifique Directe), 2010

The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in nanoscience. In this work, capillary effect was used to fill double wall carbon nanotubes (DWCNTs) with trigonal Tellurium. The samples are characterized by high resolution transmission electronic microscopy and Raman spectroscopy. In order to investigate their structural stability and unravel the differences induced by intershell interactions, unpolarized Raman spectra of radial and tangential modes of DWCNTs filled with 1D nanocrystalline Te excited with 514 nm were studied at room temperature and high pressure. Up to 11 GPa we found a pressure coefficient of 3.7 cm À1 GPa À1 for the internal tube and 7 cm À1 GPa À1 for the external tube. In addition, the tangential band of the external and internal tubes broaden and decrease in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tube (at least up 11 GPa). No pressure-induced structural phase transition was observed in the studied range.

Electron-Phonon Coupling in Rare Earth Compounds

Acta Physica Polonica A, 1996

Tle variation hi electron-phonon coupling strength for rare earth ions has been studied by measuring vibronic transition probabilities and temperature dependent line broadening for a large number of rare earth ions in differennt host lattices. The results show a large variation in the electron-phonon coupling strength (almost three orders of magnitude) and a remarkable trend: the coupling is strong for ions in the beginning and at the end of the lanthanide series and weak in the middle. In covalent host lattices the coupling is much stronger than in ionic host lattices. An explanation of the results is given and tle consequences of the variation of the electron-phonon coupling strength on phenomena like multiphonon relaxation, energy transfer and cooperative luminescence are discussed.

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Pressure-induced quenching of the charge-density-wave state in rare-earth tritellurides observed by x-ray diffraction

Physical Review B, 2009

Pressure dependence of the single particle excitation in the charge-density-wave CeTe3 system

Physical Review B, 2009

We present data on the pressure dependence at 300 K of the optical reflectivity of CeTe 3 , which undergoes a charge-density-wave ͑CDW͒ phase transition well above room temperature. The collected data cover an unprecedented broad spectral range from the infrared up to the ultraviolet, which allows a robust determination of the gap as well as of the fraction of the Fermi surface affected by the formation of the CDW condensate. Upon compressing the lattice there is a progressive closing of the gap, inducing a transfer of spectral weight from the gap feature into the Drude component. At frequencies above the CDW gap we also identify a power-law behavior, consistent with findings along the RTe 3 series ͑i.e., chemical pressure͒ and suggestive of a Tomonaga-Luttinger liquid scenario at high-energy scales. This set of data is placed in the context of our previous investigations of this class of materials and allows us to revisit important concepts for the physics of CDW state in layeredlike two-dimensional systems.

Single-Particle and Collective Mode Couplings Associated with 1-and 2-Directional Electronic Ordering in Metallic RTe3 (R=Ho,Dy,Tb)

Physical Review Letters, 2008

The coupling of phonons with collective modes and single-particle gap excitations associated with one (1d) and two-directional (2d) electronically-driven charge-density wave (CDW) ordering in metallic RTe3 is investigated as a function of rare-earth ion chemical pressure (R=Tb, Dy, Ho) using femtosecond pump-probe spectroscopy. From the T-dependence of the CDW gap ∆CDW and the amplitude mode (AM) we find that while the transition to a 1d-CDW ordered state at Tc1 initially proceeds in an exemplary mean-field (MF)-like fashion, below Tc1, ∆CDW is depressed and departs from the MF behavior. The effect is apparently triggered by resonant mode-mixing of the amplitude mode (AM) with a totally symmetric phonon at 1.75 THz. At low temperatures, when the state evolves into a 2d-CDW ordered state at Tc2 in the DyTe3 and HoTe3, additional much weaker mode mixing is evident but no soft mode is observed.

Temperature dependence of resistivity at the transition to a charge density wave state in rare-earth tritellurides

Journal of Physics: Conference Series, 2019

About a half of the Fermi surface in rare-earth tritellurides RTe 3 becomes gapped below the transition to a charge-density-wave (CDW) state, as revealed by ARPES data. However, the observed jump in resistivity during the CDW transition is less than 20%. Previously this phenomenon was explained by hypothesizing a very slow evolution of CDW energy gap below transition temperature in RTe 3 compounds, which contradicts the X-ray measurements. Here we show that this weak change in resistivity can be explained in the framework of standard mean-field temperature dependence of the CDW energy gap in agreement with X-ray data. The change of resistivity caused by CDW is weak because the decrease in conducting electron density at the Fermi level is almost compensated by the decrease in their scattering rate. We calculate resistivity in Te 3 compounds using the Boltzmann transport equation and the meanfield description of the CDW state, and obtain a good agreement with experimental data.

Evidence for coupling between charge-density-wave and phonons in two-dimensional rare-earth tri-tellurides (original) (raw)

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