arXiv subjects

P. Monceau

Publications and source records attributed to P. Monceau.

At least 37 records · Page 2Linked to original sources

arXiv2015

Critical dynamics and domain motion from permittivity of the electronic ferroelectric (TMTTF)2AsF6

The quasi one-dimensional organic conductor (TMTTF)2AsF6 shows the charge ordering transition at Tc101K to a state of the ferroelectric Mott insulator which is still well conducting. We present and interpret the experimental data on the gigantic dielectric response in the vicinity of TCO, concentrating on the frequency dependence of the inverse $1/ε$ of the complex permittivity $ε=ε^\prime+iε^{\prime\prime}$. Surprisingly for a ferroelectric, we could closely approach the 2nd order phase transition and to deeply reach the critical dynamics of the polarization. We could analyse the critical slowing-down when approaching Tc from both sides and to extract the anomalous power law for the frequency dependence of the order parameter viscosity. Moreover, below Tc we could extract a sharp absorption feature coming from a motion of domain walls which shows up at a frequency well below the relaxation rate.

cond-mat.str-el↗

arXiv2013

Spontaneous breaking of isotropy observed in the electronic transport of rare-earth tritellurides

We show that the isotropic conductivity in the normal state of rare-earth tritelluride RTe_3 compounds is broken by the occurrence of the unidirectional charge density wave (CDW) in the (a,c) plane below the Peierls transition temperature. In contrast with quasi-one-dimensional systems, the resistivity anomaly associated with the CDW transition is strong in the direction perpendicular to the CDW wave vector Q (a-axis) and very weak in the CDW wave vector Q direction (c-axis). We qualitatively explain this result by calculating the electrical conductivity for the electron dispersion with momentum-dependent CDW gap as determined by angle-resolved photoemission spectroscopy (ARPES).

cond-mat.str-el↗

arXiv2013

Quantum critical point and superconducting dome in the pressure phase diagram of o-TaS3

We measure the electrical resistance of o-TaS3 between 1K and 300K under pressures up to 20GPa. We observe a gradual decrease of the charge density wave transition temperature with increasing pressure P following a mean-field quantum fluctuation power law with a quantum critical point at a pressure Pc = 11.5GPa. Around the quantum critical point we observe a superconducting dome with a maximum superconducting transition temperature Tc = 3.1K. Such dome is similar to superconducting domes around other types of order suggesting that the QCP is directly responsible for the enhancement of superconductivity through a universal mechanism still not well understood.

cond-mat.supr-con↗

arXiv2013

Aharonov-Bohm resistance magneto-oscillations on single-nanohole graphite and graphene structures

Graphene is a stable single atomic layer material exhibiting two-dimensional electron gas of massless Dirac fermions of high mobility. One of the intriguing properties of graphene is a possibility of realization of the Tamm-type edge states. These states differ from the usual surface states caused by defects, impurities and other imperfections at the edge of the system, as well as they differ from the magnetic edge states caused by skipping cyclotron orbits. The Tamm states result from breaking of periodic crystal potential at the edge, they can exist even at zero magnetic field and form a conducting band. Until recently those states have been observed in graphene only by local STM technique and there were no direct experiments on their contribution to transport measurements. Here we present the experiments on Aharonov-Bohm (AB) oscillations of resistance in a single-nanohole graphite and graphene structures, it indicates the presence of conducting edge states cycling around nanohole. An estimation show the penetration depth of the edge states to be as short as about 2 nm. The oscillations persist up to temperature T=115 K and the T-range of their existence increases with a decrease of the nanohole diameter. The proposed mechanism of the AB oscillations based on the resonant intervalley backscattering of the Dirac fermions by the nanohole via the Tamm states. The experimental results are consistent with such a scenario. Our findings show a way towards interference devices operating at high temperatures on the edge states in graphene

cond-mat.mes-hall↗

arXiv2013

Interlayer tunneling spectroscopy of graphite at high magnetic field oriented parallel to the layers

Interlayer tunneling in graphite mesa-type structures is studied at a strong in-plane magnetic field $H$ up to 55 T and low temperature $T=1.4$ K. The tunneling spectrum $dI/dV$ vs. $V$ has a pronounced peak at a finite voltage $V_0$. The peak position $V_0$ increases linearly with $H$. To explain the experiment, we develop a theoretical model of graphite in the crossed electric $E$ and magnetic $H$ fields. When the fields satisfy the resonant condition $E=vH$, where $v$ is the velocity of the two-dimensional Dirac electrons in graphene, the wave functions delocalize and give rise to the peak in the tunneling spectrum observed in the experiment.

cond-mat.mes-hall↗

arXiv2013

Electronic Instability in a Zero-Gap Semiconductor: the Charge-Density Wave in (TaSe4)2I

We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)2I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in the non-distorted structure, with non-negligible interchain coupling. Theory and experiment support a Peierls-like scenario for the CDW formation below T_CDW = 263 K, where the incommensurability is a direct consequence of the finite interchain coupling. The formation of small polarons, strongly suggested by the ARPES data, explains the puzzling semiconductor-to-semiconductor transition observed in transport at T_CDW.

cond-mat.str-el↗

arXiv2013

Dynamical transport properties of NbSe$_3$ with simultaneous sliding of both charge density waves

Measurements of the nonlinear conductivity in NbSe$_3$ when the high-T and the low-T charge-density waves (CDWs) are simultaneously sliding have been performed. It is shown that the threshold electric field, $E_{t1}$, for depinning the high-T CDW increases 4 - 5 times at the temperature at which the low-T CDW is formed, indicating the strong pinning effect resulting from the interaction between both CDWs. Under application of a radio-frequency (rf) field, Shapiro steps are never observed simultaneously for both CDWs. At the electric field less then one for high-T CDW sliding only Sapiro steps for low-T CDW were observed, and at higher field only Shapiro steps for high-T CDW exist.

cond-mat.str-el↗

arXiv2012

Sliding charge-density-wave in two-dimensional rare-earth tellurides

Nonlinear transport properties are reported in the layered DyTe$_3$ compound at temperature below the charge-density-wave (CDW) transition, $T_P=302$ K. Conductivity is increasing sharply above the threshold electric field. Under application of a rf field Shapiro steps are clearly observed. These features demonstrate for the first time CDW sliding in two-dimensional compounds.

cond-mat.str-el↗

arXiv2012

Transverse conductivity in the sliding CDW state of NbSe_3

The dynamical properties of longitudinal and transverse conduction of NbSe$_3$ single-crystals have been simultaneously studied when the current is applied along the b axis (chain direction). In the vicinity of the threshold electric field for CDW sliding, the transverse conduction sharply decreases. When a rf field is applied, voltage Shapiro steps for longitudinal transport are observed as usual, but also current Shapiro steps in the transverse direction. The possible mechanisms of this effect are discussed.

cond-mat.str-el↗

arXiv2009

Possible Fractional Quantum Hall Effect in Graphite

Measurements of basal plane longitudinal rho_b(B) and Hall rho_H(B) resistivities were performed on highly oriented pyrolytic graphite (HOPG) samples in pulsed magnetic field up to B = 50 T applied perpendicular to graphene planes, and temperatures 1.5 K < T < 4.2 K. At B > 30 T and for all studied samples, we observed a sign change in rho_H(B) from electron- to hole-like. For our best quality sample, the measurements revealed the enhancement in rho_b(B) for B > 34 T (T = 1.8 K), presumably associated with the field-driven charge density wave or Wigner crystallization transition. Besides, well defined plateaus in rho_H(B) were detected in the ultra-quantum limit revealing the signatures of fractional quantum Hall effect in graphite.

cond-mat.mes-hall↗

arXiv2007

Equilibrium Low Temperature Heat Capacity of the Spin Density Wave compound (TMTTF)2 Br: effect of a Magnetic Field

We have investigated the effect of the magnetic field (B) on the very low-temperature equilibrium heat capacity ceq of the quasi-1 D organic compound (TMTTF)2Br, characterized by a commensurate Spin Density Wave (SDW) ground state. Below 1K, ceq is dominated by a Schottky-like contribution, very sensitive to the experimental time scale, a property that we have previously measured in numerous DW compounds. Under applied field (in the range 0.2- 7 T), the equilibrium dynamics, and hence ceq extracted from the time constant, increases enormously. For B = 2-3 T, ceq varies like B2, in agreement with a magnetic Zeeman coupling. Another specific property, common to other Charge/Spin density wave (DW) compounds, is the occurrence of metastable branches in ceq, induced at very low temperature by the field exceeding a critical value. These effects are discussed within a generalization to SDWs in a magnetic field of the available Larkin-Ovchinnikov local model of strong pinning. A limitation of the model when compared to experiments is pointed out.

cond-mat.dis-nn↗

arXiv2006

Anomalous asymmetry of magnetoresistance in NbSe$_3$ single crystals

A pronounced asymmetry of magnetoresistance with respect to the magnetic field direction is observed for NbSe$_3$ crystals placed in a magnetic field perpendicular to their conducting planes. It is shown that the effect persists in a wide temperature range and manifests itself starting from a certain magnetic induction value $B_0$, which at $T=4.2$ K corresponds to the transition to the quantum limit, i.to the state where the Landay level splitting exceeds the temperature.

cond-mat.str-el↗

arXiv2005

Recent results on energy relaxation in disordered charge and spin density waves

We briefly review different approaches used recently to describe collective effects in the strong pinning model of disordered charge and spin density waves, in connection with the CRTBT very low temperature heat relaxation experiments.

cond-mat.dis-nn↗

arXiv2004

The c-axis transport in naturally-grown Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ cross-whisker junctions

We studied the c-axis transport of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) cross-whisker junctions formed by annealing ``naturally'' formed whisker junctions. These frequently appear during growth when the $ab$-faces of neighboring whiskers come in contact. We obtained Fraunhofer patterns of the cross-junction critical currents in a parallel magnetic field, and found a sharp increase in the quasiparticle tunneling conductance at $eV=50-60$ mV, indicating high junction quality. For our weak junctions, the interface critical current density is about 0.03 of the critical current density across the stack of bulk intrinsic junctions, as is the room temperature conductivity, and is independent of the twist angle, in contrast to most of the data reported on ``artificial'' cross-whisker junctions [Y. Takano {\it et al.}, Phys. Rev. B {\bf 65}, 140513(R) (2002)]. Our results provide strong evidence of incoherent interface tunneling and for at least a small s-wave order parameter component in the bulk of Bi2212 for $T\le T_c$. They are also consistent with the bicrystal twist experiments of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)].

cond-mat.supr-con↗

arXiv2003

Ferroelectric Mott-Hubbard phase in organic conductors

We present key issues of related phenomenons of the Ferroelectricity and the Charge Disproportionation in organic metals. In (TMTTF_2X the dielectric susceptibility demonstrates clear cases of the ferroelectric and anti-ferroelectric phase transitions. Both the susceptibility and the conductivity prove independence and occasional coexistence of "structurless" ferroelectric transitions and usual "anionic" ones. Their sequence gives access to physics of three types of solitons emerging upon cooling via several steps of symmetry breaking. The theory invokes a concept of the Combined Mott-Hubbard State which focuses upon weak processes of electronic Umklapp scattering coming from both the build-in nonequivalence of bonds and the spontaneous one of sites. We propose that the charge ordering in its form of the ferroelectricity exists hiddenly even in the Se subfamily (TMTSF)_2X, giving rise to the unexplained yet low frequency optical peak and the enhanced pseudogap.

cond-mat.str-el↗

arXiv2003

Evidence of 1D behaviour of He$^4$ confined within carbon-nanotube bundles

We present the first low-temperature thermodynamic investigation of the controlled physisorption of He$^{4}$ gas in carbon single-wall nanotube (SWNT) samples. The vibrational specific heat measured between 100 mK and 6 K demonstrates an extreme sensitivity to outgassing conditions. For bundles with a few number of NTs the extra contribution to the specific heat, C$_{ads}$, originating from adsorbed He$^{4}$ at very low density displays 1D behavior, typical for He atoms localized within linear channels as grooves and interstitials, for the first time evidenced. For larger bundles, C$_{ads}$ recovers the 2D behaviour akin to the case of He$^{4}$ films on planar substrates (grafoil).

cond-mat.mtrl-sci↗

arXiv2002

Unconventional magnetoresistance in long InSb nanowires

Magnetoresistance in long correlated nanowires of degenerate semiconductor InSb in asbestos matrix (wire diameter of around 5 nm, length 0.1 - 1 mm) is studied over temperature range 2.3 - 300 K. At zero magnetic field the electric conduction $G$ and the current-voltage characteristics of such wires obey the power laws $G\propto T^α$, $I\propto V^β$, expected for one-dimensional electron systems. The effect of magnetic field corresponds to a 20% growth of the exponents $α$, $β$ at H=10 T. The observed magnetoresistance is caused by the magnetic-field-induced breaking of the spin-charge separation and represents a novel mechanism of magnetoresistance.

cond-mat.str-el↗

arXiv2002

Fractional power-law susceptibility and specific heat in low temperature insulating state of o-TaS_{3}

Measurements of the magnetic susceptibility and its anisotropy in the quasi-one-dimensional system o-TaS_{3} in its low-T charge density wave (CDW) ground state are reported. Both sets of data reveal below 40 K an extra paramagnetic contribution obeying a power-law temperature dependence χ(T)=AT^{-0.7}. The fact that the extra term measured previously in specific heat in zero field, ascribed to low-energy CDW excitations, also follows a power law C_{LEE}(0,T)=CT^{0.3}, strongly revives the case of random exchange spin chains. Introduced impurities (0.5% Nb) only increase the amplitude C, but do not change essentially the exponent. Within the two-level system (TLS) model, we estimate from the amplitudes A and C that there is one TLS with a spin s=1/2 localized on the chain at the lattice site per cca 900 Ta atoms. We discuss the possibility that it is the charge frozen within a soliton-network below the glass transition T_{g}~40 K determined recently in this system.

cond-mat↗