arXiv subjects

L. Balicas

Publications and source records attributed to L. Balicas.

At least 109 records · Page 6Linked to original sources

arXiv2003

Charge-density Waves Survive the Pauli Paramagnetic Limit

Measurements of the resistance of single crystals of (Per)$_2$Au(mnt)$_2$ have been made at magnetic fields $B$ of up to 45 T, exceeding the Pauli paramagnetic limit of $B_{\rm P}\approx 37$ T. The continued presence of non-linear charge-density wave electrodynamics at $B \geq 37$ T unambiguously establishes the survival of the charge-density wave state above the Pauli paramagnetic limit, and the likely emergence of an inhomogeneous phase analogous to that anticipated to occur in superconductors.

cond-mat.str-el↗

arXiv2003

NMR Investigation of the Organic Conductor lambda-(BETS)2FeCl4

The two-dimensional organic conductor lambda-(BETS)2FeCl4 has an unusual phase diagram as a function of temperature and magnetic field that includes a paramagnetic metal (PM) phase, an antiferromagnetic insulating (AFI) phase, and a field-induced superconducting phase [S. Uji, H. Kobayashi, L. Balicas, and James S. Brooks, Adv. Mater. 14, 243 (2002), and cited references]. Here, we report a preliminary investigation of the PM and AFI phases at 9.0 T over the temperature range 2.0-180 K that uses proton NMR measurements of the spectrum, the spin-lattice relaxation rate (1/T1), and the spin echo decay rate (1/T2). The sample is asmall single crystal whose mass is approximately 3 micrograms (approximately 2E16 protons). Its small size creates several challenges that include detecting small signals and excluding parasitic proton signals that are not from the sample [H. N. Bachman and I. F. Silvera, J. Mag. Res. 162, 417 (2003)]. These strategies and other techniques used to obtain viable signals are described.

cond-mat.str-el↗

arXiv2003

Field-tuned Collapse of an Orbital Ordered and Spin-polarized State: Colossal Magnetoresistance in Bilayered Ruthenate

Ca3Ru2O7 with a Mott-like transition at 48 K features different in-plane anisotropies of magnetization and magnetoresistance. Applying magnetic field along the magnetic easy-axis precipitates a spin-polarized state via a first-order metamagnetic transition, but does not lead to a full suppression of the Mott state, whereas applying magnetic field along the magnetic hard axis does, causing a resistivity reduction of three orders of magnitude. The colossal magnetoresistivity is attributed to the collapse of the orbital ordered and spin-polarized state. Evidence for a density wave is also presented.

cond-mat.str-el↗

arXiv2003

Determination of the Fermi Surface of MgB$_2$ by the de Haas-van Alphen effect

We report measurements of the de Haas-van Alphen effect for single crystals of MgB$_2$, in magnetic fields up to 32 Tesla. In contrast to our earlier work, dHvA orbits from all four sheets of the Fermi surface were detected. Our results are in good overall agreement with calculations of the electronic structure and the electron-phonon mass enhancements of the various orbits, but there are some small quantitative discrepancies. In particular, systematic differences in the relative volumes of the Fermi surface sheets and the magnitudes of the electron-phonon coupling constants could be large enough to affect detailed calculations of T$_{c}$ and other superconducting properties.

cond-mat.supr-con↗

arXiv2003

Quantum Oscillations, Colossal Magnetoresistance and Magnetoelastic Interaction in Bilayered Ca3Ru2O7

We report magnetic and inter-plane transport properties of Ca3Ru2O7 at high magnetic fields and low temperatures. Ca3Ru2O7 with a bilayered orthorhombic structure is a Mott-like system with a narrow charge gap of 0.1eV. Of a host of unusual physical phenomena revealed in this study, a few are particularly intriguing: (1) a collapse of the c-axis lattice parameter at a metal-nonmetal transition, TMI (=48 K), and a rapid increase of TMI with low uniaxial pressure applied along the c-axis; (2) quantum oscillations in the gapped, nonmetallic state for 20 mK<T<6.5 K; (3) tunneling colossal magnetoresistance, which yields a precipitate drop in resistivity by as much as three orders of magnitude; (4) different in-plane anisotropies of the colossal magnetoresistance and magnetization. All results appear to indicate a highly anisotropic ground state and a critical role of coupling between lattice and magnetism. The implication of these phenomena is discussed.

cond-mat.str-el↗

arXiv2003

Competing Ground States in Triple-layered Sr4Ru3O10: Verging on Itinerant Ferromagnetism with Critical Fluctuations

Sr4Ru3O10 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.

cond-mat.str-el↗

arXiv2003

First order transition from correlated electron semiconductor to ferromagnetic metal in single crystalline FeSi1-xGex

The phase diagram of FeSi1-xGex, obtained from magnetic, thermal and transport measurements on single crystals, shows a first-order transition from a correlated electron semiconductor to a ferromagnetic metal at a critical concentration, x ~ 0.25. The gap of the insulating phase strongly decreases with x. The specific heat coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with a correlation induced insulator-metal transition in conjunction with disorder on the Si/Ge ligand site.

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arXiv2002

High magnetic field-induced insulating phase in an organic conductor

We report electrical transport, skin depth, and magnetocaloric measurements in the tau-series of organic conductors at very high magnetic fields. Above 36 T these materials show a magnetic field induced first order phase transition from a metallic to an insulating state. The transition, which is a bulk thermodynamic phenomenon, does not follow the conventional prescription for field induced phase transitions in organic conductors.

cond-mat↗

arXiv2002

Intersite coupling effects in a Kondo lattice

The La dilution of the Kondo lattice CeCoIn_5 is studied. The scaling laws found for the magnetic susceptibility and the specific heat reveal two well-separated energy scales, corresponding to the single impurity Kondo temperature T_K and an intersite spin-liquid temperature T^*. The Ce-dilute alloy has the expected Fermi liquid ground state, while the specific heat and resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which scales with T^*. These observations indicate that the screening of the magnetic moments in the lattice involves antiferromagnetic intersite correlations with a larger energy scale in comparison with the Kondo impurity case.

cond-mat.str-el↗

arXiv2002

Complex Quantum Phenomena in a Bilayered Calcium Ruthenate

Ca$_3$Ru$_2$O$_7$ undergoes an antiferromagnetic transition at $T_{\text{N}}=56 $K, followed by a Mott-like (MI) transition at $T_{\text{MI}}=48$ K. This nonmetallic ground state, with a charge gap of 0.1 eV, is suppressed by a highly anisotropic metamagnetic transition that leads to a fully spin-polarized metallic state. We report the observation of Shubnikov-de Haas oscillations in the \textit{gapped} state, colossal magnetoresistance in the inter-plane resistivity with a large anisotropy different from that observed in the magnetization, and non-Fermi liquid behavior in the metallic state at high magnetic fields.

cond-mat.str-el↗

arXiv2002

Disorder-driven magnetic field-dependent phases in an organic conductor

We report inter-plane ($R_{zz}$) electrical transport measurements in the \tp series of organic conductors at very high magnetic fields. In the field range between 36 and 60 T $R_{zz}$ shows a very hysteretic first order phase transition from metallic to an insulating state. This transition does not affect the Shubnikov-de-Haas oscillations associated with the two-dimensional (2D) Fermi surface. We argue that this transition originates from inter-plane disorder which gives rise to incoherent transport along the least conducting axis. We conclude that this system becomes a strictly 2D Fermi-liquid at high magnetic fields.

cond-mat.str-el↗

arXiv2001

Superconductivity in an organic insulator at very high magnetic fields

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor $λ$-(BETS)$_2$FeCl$_4$. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T, and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field {\em compensates} the exchange field of aligned Fe$^{3+}$ ions. We further argue that the Fe$^{3+}$ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state

cond-mat.str-el↗

arXiv2000

Electronic Structure of Novel Cation-Radical Salts in High Magnetic Fields

Two organic conducting materials, where unusual aspects of their composition play important roles, are explored: beta''-(BEDT-TTF)2SF5XSO3 which exhibits superconductivity, or a metal-insulator transition (for X=CH2CF2 or CHF respectively), and tau-(P-S, S -DMEDT-TTF)2 (AuBr2) (AuBr2)y which exhibits a large, hysteretic, negative magnetoresistance. Detailed angular dependent magnetoresistance studies that allow a tomographic view of the electronic structure of these materials with increasing magnetic fields are presented.

cond-mat.str-el↗

arXiv2000

Effect of controlled disorder on quasiparticle thermal transport in Bi$_2$Sr$_2$CaCu$_2$O$_8$

Low temperature thermal conductivity, $κ$, of optimally-doped Bi2212 was studied before and after the introduction of point defects by electron irradiation. The amplitude of the linear component of $κ$ remains unchanged, confirming the universal nature of heat transport by zero-energy quasiparticles. The induced decrease in the absolute value of $κ$ at finite temperatures allows us to resolve a nonuniversal term in $κ$ due to conduction by finite-energy quasiparticles. The magnitude of this term provides an estimate of the quasiparticle lifetime at subkelvin temperatures.

cond-mat.supr-con↗

arXiv2000

Magnetic field-dependent interplay between incoherent and Fermi liquid transport mechanisms in low-dimensional tau phase organic conductors

We present an electrical transport study of the 2-dimensional (2D) organic conductor tau-(P-(S,S)-DMEDT-TTF)_2(AuBr)_2(AuBr_2)_y (y = 0.75) at low temperatures and high magnetic fields. The inter-plane resistivity rho_zz increases with decreasing temperature, with the exception of a slight anomaly at 12 K. Under a magnetic field B, both rho_zz and the in-plane resistivity plane rho_xx show a pronounced negative and hysteretic magnetoresistance with Shubnikov de Haas (SdH)oscillations being observed in some (high quality)samples above 15 T. Contrary to the predicted single, star-shaped, closed orbit Fermi surface from band structure calculations (with an expected approximate area of 12.5% of A_FBZ), two fundamental frequencies F_l and F_h are detected in the SdH signal. These orbits correspond to 2.4% and 6.8% of the area of the first Brillouin zone(A_FBZ), with effective masses F_l = 4.0 +/- 0.5 and F_h = 7.3 +/- 0.1. The angular dependence, in tilted magnetic fields of F_l and F_h, reveals the 2D character of the FS and Angular dependent magnetoresistance (AMRO) further suggests a FS which is strictly 2-D where the inter-plane hopping t_c is virtually absent or incoherent. The Hall constant R_xy is field independent, and the Hall mobility increases by a factor of 3 under moderate magnetic fields. Our observations suggest a unique physical situation where a stable 2D Fermi liquid state in the molecular layers are incoherently coupled along the least conducting direction. The magnetic field not only reduces the inelastic scattering between the 2D metallic layers, but it also reveals the incoherent nature of interplane transport in the AMRO spectrum. The apparent ferromagnetism of the hysteretic magnetoresistance remains an unsolved problem.

cond-mat.str-el↗

arXiv2000

On the absence of spin-splitting in alpha-(BEDT-TTF)2KHg(SCN)4

We report the results of a detailed study of the field orientation-dependence of the de Haas-van Alphen waveform in $α$-(BEDT-TTF)$_2$KHg(SCN)$_4$. By considering the field orientation-dependence of the sign and phase of the fundamental $α$ frequency, at fields both well above and below the kink transition field, it is found that a single value for the product of the effective mass with the electron {\it g}-factor can explain the experimental data deep within both the high magnetic field and low magnetic field phases. This implies that spin-splitting does not occur within the low magnetic field phase until the angle between the magnetic field and the normal to the conducting planes is $\sim$~42$^\circ$. This finding contrasts greatly with that recently published by Sasaki and Fukase, implying that electron-electron interactions do not play a significant role in the formation of the charge-density wave ground state. The manner in which the amplitude of the waveform of the oscillations is damped within the low magnetic field phase is indicative of a non harmonically indexed reduction of the amplitude, thereby eliminating both magnetic breakdown and impurity scattering as dominant damping mechanisms within this phase. Meanwhile, the presence of a large amplitude second harmonic within the low magnetic field phase that has a negative sign over a broad range of angles can only be explained by the frequency doubling effect.

cond-mat.str-el↗

arXiv2000

Transverse and in-plane modification of superconductivity and electronic structure in the quasi-two dimensional organic conductor $κ$--(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$ by uniaxial stress

We have employed uniaxial stress along the principal axes of the quasi-two dimensional organic superconductor $κ$--(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$. The lattice anisotropy is thereby altered, with corresponding changes in the intermolecular transfer energies. The effect of uniaxial stress on the superconducting transition temperature $T_{c}$ and critical field $B_{c2}$ is found to be anisotropic.There is an indication of an increase in $T_{c}$ and $B_{c2}$ for in-plane stress, but both parameters decrease rapidly for transverse (inter-plane) stress. Magnetotransport studies reveal stress-induced changes in the Fermi surface through the observation of the Shubnikov de Haas oscillations. The stress dependence of a resistive anomaly in the magnetoresistance, which is associated with the critical field $B_{c2}$, is also investigated. We discuss the experimental findings in the context of recent phenomenological and theoretical treatments of quasi-two dimensional systems where the anisotropic triangular lattice Hubbard model has been used to treat two-dimensional superconductors.

cond-mat.supr-con↗

arXiv2000

Shubnikov-de Haas effect and Yamaji oscillations in the antiferromagnetically ordered organic superconductor k-(BETS)2FeBr4: A Fermiology study

Shubnikov-De Haas effect (SdH) effect and angular dependent magnetoresistance oscillations (AMRO) were observed in the organic superconductor: $κ$-(BETS)$_2$FeBr$_4$. In contrast to its isostructural compound $κ-(BETS)$_2$FeCl$_4$, SdH oscillations, for fields perpendicular to the conducting planes, reveal three Fermi Surface (FS) closed orbits $α$, $β$, and $γ$ whose cross sectional areas are 19.8 %, 99.9 %, and 2.4 % of the first Brillouin zone, respectively. The conduction electron effective masses were found to be: $μ_α = (4.7 \pm 0.2)$ m$_e$, $μ_β = (8.0 \pm 1.0)$ m$_e$, and $μ_γ = (2.0 \pm 0.2)$ m$_e$. The observation of a $γ$ orbit is not expected from band structure calculations, $μ_β$ is among the heaviest masses ever reported for an organic conductor. The observed Yamaji-like AMRO indicates a 2-D closed FS, warped along the $k_z$ direction.

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