L. Balicas - Academia.edu (original) (raw)

Papers by L. Balicas

$Research paper thumbnail of Multiband superconductivity in LaFeAsO_{0.9}F_{0.1} single crystals probed by high-field vortex torque magnetometry$

Physical Review B, 2011

To probe manifestations of multiband superconductivity in oxypnictides, we measured the angular d... more To probe manifestations of multiband superconductivity in oxypnictides, we measured the angular dependence of the magnetic torque τ (θ) in the mixed state of LaO0.9F0.1FeAs single crystals as a function of temperature T and magnetic fields H up to 18 T. The paramagnetic contribution of the Fe ions is properly treated in order to extract the effective mass anisotropy parameter γ = (mc/m ab) 1/2 from τ (θ). We show that γ depends strongly on both T and H, reaching a maximum value of ∼ 10 followed by a decrease towards values close to 1 as T is lowered. The observed field dependencies of the London penetration depth λ ab and γ suggest the onset of suppression of a superconducing gap at H ≈ Hc2/3.

Physical Review B, 2003

Sr 4 Ru 3 O 10 is characterized by a sharp metamagnetic transition and ferromagnetic behavior occ... more Sr 4 Ru 3 O 10 is characterized by a sharp metamagnetic transition and ferromagnetic behavior occurring within the basal plane and along the c-axis, respectively. Resistivity at magnetic field, B, exhibits low-frequency quantum oscillations when B||c-axis and large magnetoresistivity accompanied by critical fluctuations driven by the metamagnetism when B⊥c-axis. The complex behavior evidenced in resistivity, magnetization and specific heat presented is not characteristic of any obvious ground states, and points to an exotic state that shows a delicate balance between fluctuations and order.

dichalcogenides (TMDCs) like MoS2, WS2, and WSe2 were successfully used as light sensors. The sam... more dichalcogenides (TMDCs) like MoS2, WS2, and WSe2 were successfully used as light sensors. The samples were structurally characterized by Raman spectroscopy, AFM, SEM, and HRTEM. The produced samples consisted of few layered sheets possessing up to 10 layers obtained by different synthetic or isolation methods including low-pressure CVD, atmospheric-pressure CVD and mechanical exfoliation. Current-voltage (I-V) and photo response measurements carried out by connecting the TMDC layered sample with Au/Ti contacts. The photocurrent measurements were carried out at different wavelengths from 400 to 800 nm. The results indicate that the electrical response strongly depends on the photon energy from the excitation lasers. In addition, it was found that the photocurrent varied non-linearly with the incident power, and the generated photocurrent in the WS 2 samples varied as a squared root of the incident power. The response time of the devices was measured and resulted in the order of few milliseconds. Because of its fast response, good responsivity and stability few-layered TMDCs are strong candidates for constructing novel optoelectronic devices.

Physical Review B, 2012

The study of two-dimensional (2D) electronic systems is of great fundamental significance in phys... more The study of two-dimensional (2D) electronic systems is of great fundamental significance in physics. Atomic layers containing hybridized domains of graphene and hexagonal boron nitride (h-BNC) constitute a new kind of disordered 2D electronic system. Magneto-electric transport measurements performed at low temperature in vapor phase synthesized h-BNC atomic layers show a clear and anomalous transition from an insulating to a metallic behavior upon cooling. The observed insulator to metal transition can be modulated by electron and hole doping and by the application of an external magnetic field. These results supported by ab-initio calculations suggest that this transition in h-BNC has distinctly different characteristics when compared to other 2D electron systems and is the result of the coexistence between two distinct mechanisms, namely, percolation through metallic graphene networks and hopping conduction between edge states on randomly distributed insulating h-BN domains.

Physical Review B, 2005

We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al doped crystals of M... more We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al doped crystals of MgB2. We have measured crystals with ∼ 7.5% Al which have a Tc of 33.6 K, (∼ 14% lower than pure MgB2). dHvA frequencies for the σ tube orbits in the doped samples are lower than in pure MgB2, implying a 16 ± 2% reduction in the number of holes in this sheet of Fermi surface. The mass of the quasiparticles on the larger σ orbit is lighter than the pure case indicating a reduction in electron-phonon coupling constant λ. These observations are compared with band structure calculations, and found to be in excellent agreement.

$Research paper thumbnail of Possible Bose-Einstein condensate of magnons in single-crystalline Pb_{2}V_{3}O_{9}$

Physical Review B, 2010

We report the growth and the characterization of single crystals of the S =1/ 2 spin-dimer compou... more We report the growth and the characterization of single crystals of the S =1/ 2 spin-dimer compound Pb 2 V 3 O 9. Magnetic-susceptibility, torque magnetometry, heat-capacity, and muon-spin-relaxation measurements provide evidence for a field-induced Bose-Einstein condensate of magnons in this system. At low temperatures, the field-dependent phase boundary between the dimerized and the condensed state is well described by the expression T Ã ϰ ͑H − H c1 ͒ 1/ , with = ͑2.00Ϯ 0.04͒.

Physica B: Condensed Matter, 2001

ABSTRACT

Journal of Physics: Condensed Matter, 2011

The low temperature behaviour of single crystalline SrHo(2)O(4) has been characterized by dc magn... more The low temperature behaviour of single crystalline SrHo(2)O(4) has been characterized by dc magnetic susceptibility, heat capacity, and neutron scattering experiments. Our results show that despite the lack of magnetic long-ranged ordering in the presence of strong antiferromagnetic correlations, SrHo(2)O(4) does not order down to 1.8 K. Elastic neutron scattering experiments show prominent magnetic diffuse scattering correlated with a broad feature in the dc susceptibility at T = 4 K, indicative of magnetic short-ranged ordering of the Ho(3) spins. Inelastic neutron scattering shows the presence of five crystal field levels up to 80 K in energy, in agreement with the integration of the magnetic specific heat component yielding Rln5 entropy release. The magnetic short-ranged ordering is fitted to a nearest neighbour interaction model with good agreement.

Journal of Magnetism and Magnetic Materials, 2007

Torque magnetisation data are presented which probe the line of second order phase transitions ap... more Torque magnetisation data are presented which probe the line of second order phase transitions approaching the Bose-Einstein condensation (BEC) quantum critical point (QCP) in BaCuSi 2 O 6. Results reveal that as the temperature is lowered, the phase transition is increasingly dominated by quantum rather than thermal fluctuations near the QCP.

$Research paper thumbnail of Topological properties of possible Weyl superconducting states of URu $ _\ mathbf {2} $ Si $ _\ mathbf {2} $$

We show that the current thermodynamic measurements in the superconducting phase of URu2Si2 are c... more We show that the current thermodynamic measurements in the superconducting phase of URu2Si2 are compatible with two distinct singlet chiral paired states kz(kx ± iky) and (kx ± iky) 2. Depending on the locations of the Fermi surface in the hidden ordered phase, both of these chiral d-wave pairings can support point and line nodes. Despite possessing similar low temperature thermodynamic properties, these two pairings are topologically distinguished by their respective orbital angular momentum projections along the c-axis, m = ±1 and m = ±2. The point nodes of these states act as the monopoles and the anti-monopoles of the Berry's gauge flux of charge ±m, which are separated in the momentum space along the c axis. As a result, the Berry's flux through the ab plane equals m. Consequently, the point nodes of kz(kx + iky) and (kx ± iky) 2 states respectively realize the Weyl and the double-Weyl fermions, with chemical potential exactly tuned at the Fermi point, due to the charge conjugation symmetry. These topologically nontrivial point nodes, give rise to m copies of protected spin degenerate, chirally dispersing surface states on the ca and the cb planes, which carry surface current, and their energies vanish at the Fermi arcs. In contrast, a line node acts as the momentum space vortex loop, and gives rise to the zero energy, dispersionless Andreev bound states on the surfaces parallel to the plane enclosed by the line node. The Berry's flux through the ab plane gives rise to anomalous spin Hall and thermal Hall conductivities, and various magnetoelectric effects. A clear determination of the bulk invariant can only be achieved by probing the pairing symmetry via a corner Josephson junction measurement, and Fourier transformed STM measurements of the Fermi arcs. Therefore, we identify URu2Si2 as a promising material for realizing gapless topological superconductivity in three spatial dimensions.

Proceedings of the National Academy of Sciences, 2020

Stacking layers of atomically thin transition-metal carbides and two-dimensional (2D) semiconduct... more Stacking layers of atomically thin transition-metal carbides and two-dimensional (2D) semiconducting transition-metal dichalcogenides, could lead to nontrivial superconductivity and other unprecedented phenomena yet to be studied. In this work, superconducting α-phase thin molybdenum carbide flakes were first synthesized, and a subsequent sulfurization treatment induced the formation of vertical heterolayer systems consisting of different phases of molybdenum carbide—ranging from α to γ′ and γ phases—in conjunction with molybdenum sulfide layers. These transition-metal carbide/disulfide heterostructures exhibited critical superconducting temperatures as high as 6 K, higher than that of the starting single-phased α-Mo2C (4 K). We analyzed possible interface configurations to explain the observed moiré patterns resulting from the vertical heterostacks. Our density-functional theory (DFT) calculations indicate that epitaxial strain and moiré patterns lead to a higher interfacial densit...

The intercalated graphite superconductor CaC6 with Tc ~ 11.5 K has been synthesized and character... more The intercalated graphite superconductor CaC6 with Tc ~ 11.5 K has been synthesized and characterized with magnetoresistance measurements. Above the transition, the resistivity follows a T^2 dependence up to 50 K, which suggests Fermi liquid behavior. Above 50 K, the data can be fit to the Bloch-Gruneisen model providing a Debye temperature of theta = 263 K. By using McMillan formula, we estimate the electron-phonon coupling constant of lambda = 0.85 which places this material in the intermediate-coupling regime. The upper critical field is determined parallel and perpendicular to the superconducting planes, and the dependence of the upper critical field as a function of angle suggests that this is a quasi-2D superconductivity. All of these measurements are consistent with BCS-like superconductivity.

Philosophical Magazine

We present detailed results of the field evolution of the de Haas-van Alphen (dHvA) effect in CeR... more We present detailed results of the field evolution of the de Haas-van Alphen (dHvA) effect in CeRhIn 5. A magnetic fieldinduced reconstruction of the Fermi surface is clearly shown to occur inside the antiferromagnetic state, in an applied field of around B * 30 T, which is evidenced by the appearance of several new dHvA branches. The angular dependence of the dHvA frequencies reveals that the Fermi surfaces of CeRhIn 5 at B > B * and CeCoIn 5 are similar. The results suggest that the Ce-4f electrons in CeRhIn 5 become itinerant at B > B * due to the Kondo effect, prior to the field-induced quantum critical point (QCP) at B c0 50 T. The electronic states at the field-induced QCP are therefore different from that of the pressure-induced QCP where a dramatic Fermi surface reconstruction occurs exactly at the critical pressure, indicating that multiple types of QCP may exist in CeRhIn 5 .

AIP Conference Proceedings, 2006

Physical Phenomena At High Magnetic Fields IV, 2002

ABSTRACT

New Journal of Physics, 2004

We report recent transport and thermodynamic experiments over a wide range of temperatures for th... more We report recent transport and thermodynamic experiments over a wide range of temperatures for the Mott-like system Ca 3 Ru 2 O 7 at high magnetic fields, B (≤ 30 T). This work reveals a rich and highly anisotropic phase diagram, where applying B along the a-, band nd c-axis leads to vastly different behavior. A fully spin-polarized state via a first order metamagnetic transition is obtained for B ≥ 6 T and B||a, and colossal magnetoresistance is seen for B||b, and quantum oscillations in the resistivity are observed for B||c, respectively. The interplay of the lattice, orbital and spin degrees of freedom are believed to give rise to this strongly anisotropic behavior.

$Research paper thumbnail of <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mrow></mrow><mn>1</mn></msup></mrow><annotation encoding="application/x-tex">^{1}</annotation></semantics></math>1H-NMR spin-echo measurements of the static and dynamic spin properties in <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>λ</mi></mrow><annotation encoding="application/x-tex">\lambda</annotation></semantics></math>λ-(BETS)$_{2}$FeCl$_{4}$$ 1^{1}1H-NMR spin-echo measurements of the spin-echo decay M(2tau)M(2\tau)M(2tau) with a decay rate 1/$T_{2}$ ... more $^{1}$H-NMR spin-echo measurements of the spin-echo decay M(2tau)M(2\tau)M(2tau) with a decay rate 1/$T_{2}$ and the frequency shift Deltanu/nu0\Delta\nu/\nu_{0}Deltanu/nu0 under applied magnetic field mathbfB\mathbf{B}mathbfB$_{0}$ = 9 T along the a-axis over a temperature range 2.0$-$180 K are reported for a single crystal of the organic conductor lambda\lambdalambda-(BETS)$_{2}$FeCl$_{4}$. It provides the spin dynamic and static properties in the paramagnetic metal (PM) and antiferromagnetic insulator (AFI) states as well as across the PM$-$AFI phase transition. A large slow beat structure in the spin-echo decay is observed with a typical beat frequency of fff sim\simsim 7 kHz and it varies across the spectrum. Its origin is attributed to the 1^{1}1H$-$$^{1}$H dipole interactions rather than to the much larger dipolar field contribution from the Fe$^{3+}$ electrons (spin SSS = 5/2). A simple phenomenological model provides an excellent fit to the data. The dominant 1^{1}1H-NMR frequency shift comes from the dipolar field from the 3d Fe$...