Measuring thermal conductivity in extreme conditions: sub-Kelvin temperatures and high (27 T) magnetic fields

We present a one-heater-two-thermometer set-up for measuring thermal conductivity and electric resistivity of a bulk sample at low temperatures down to 0.1 K and in magnetic fields up to 27 Tesla. The design overcomes the difficulties emerging in the context of large water-cooled resistive magnets.Comment: 4 pages including 4 figure

On the destruction of the hidden order in URu2_2Si2_2 by a strong magnetic field

We present a study of transport properties of the heavy fermion URu$_2$Si$_2$ in pulsed magnetic field. The large Nernst response of the hidden order state is found to be suppressed when the magnetic field exceeds 35 T. The combination of resistivity, Hall and Nernst data outlines the reconstruction of the Fermi surface in the temperature-field phase diagram. The zero-field ground state is a compensated heavy-electron semi-metal, which is destroyed by magnetic field through a cascade of field-induced transitions. Above 40 T, URu$_2$Si$_2$ appears to be a polarized heavy fermions metal with a large density of carriers whose effective mass rapidly decreases with increasing magnetic polarization.Comment: published versio

Evidence for a quantum phase transition in electron-doped Pr2−x_{2-x}Cex_{x}CuO4−δ_{4-\delta} from Thermopower measurements

The evidence for a quantum phase transition under the superconducting dome in the high-$T_c$ cuprates has been controversial. We report low temperature normal state thermopower(S) measurements in electron-doped Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ as a function of doping (x from 0.11 to 0.19). We find that at 2K both S and S/T increase dramatically from x=0.11 to 0.16 and then saturate in the overdoped region. This behavior has a remarkable similarity to previous Hall effect results in Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ . Our results are further evidence for an antiferromagnetic to paramagnetic quantum phase transition in electron-doped cuprates near x=0.16.Comment: 4 pages, 5 figure

Thermodynamic evidence for valley-dependent density of states in bulk bismuth

Electron-like carriers in bismuth are described by the Dirac Hamiltonian, with a band mass becoming a thousandth of the bare electron mass along one crystalline axis. The existence of three anisotropic valleys offers electrons an additional degree of freedom, a subject of recent attention. Here, we map the Landau spectrum by angle-resolved magnetostriction, and quantify the carrier number in each valley: while the electron valleys keep identical spectra, they substantially differ in their density of states at the Fermi level. Thus, the electron fluid does not keep the rotational symmetry of the lattice at low temperature and high magnetic field, even in the absence of internal strain. This effect, reminiscent of the Coulomb pseudo-gap in localized electronic states, affects only electrons in the immediate vicinity of the Fermi level. It presents the most striking departure from the non-interacting picture of electrons in bulk bismuth.Comment: 6 pages, 3 Figure

The Nernst effect and the boundaries of the Fermi liquid picture

Following the observation of an anomalous Nernst signal in cuprates, the Nernst effect was explored in a variety of metals and superconductors during the past few years. This paper reviews the results obtained during this exploration, focusing on the Nernst response of normal quasi-particles as opposed to the one generated by superconducting vortices or by short-lived Cooper pairs. Contrary to what has been often assumed, the so-called Sondheimer cancelation does not imply a negligible Nernst response in a Fermi liquid. In fact, the amplitude of the Nernst response measured in various metals in the low-temperature limit is scattered over six orders of magnitude. According to the data, this amplitude is roughly set by the ratio of electron mobility to Fermi energy in agreement with the implications of the semi-classical transport theory.Comment: Final version, Topical review for JPC

Nernst quantum oscillations in bulk semi-metals

With a widely available magnetic field of 10 T, one can attain the quantum limit in bismuth and graphite. At zero magnetic field, these two elemental semi-metals host a dilute liquid of carriers of both signs. When the quantum limit is attained, all quasi-particles are confined to a few Landau tubes. Each time a Landau tube is squeezed before definitely leaving the Fermi surface, the Nernst response sharply peaks. In bismuth, additional Nernst peaks, unexpected in the non-interacting picture, are resolved beyond the quantum limit. The amplitude of these unexpected Nernst peaks is larger in the samples with the longest electron mean-free-path.Comment: Accepted for publication in Journal of Physics: Condensed Matter's special issue on Strongly Correlated Electron Systems(SCES

Anomalous quasiparticle transport in the superconducting state of CeCoIn5

We report on a study of thermal Hall conductivity k_xy in the superconducting state of CeCoIn_5. The scaling relation and the density of states of the delocalized quasiparticles, both obtained from k_xy, are consistent with d-wave superconducting symmetry. The onset of superconductivity is accompanied by a steep increase in the thermal Hall angle, pointing to a striking enhancement in the quasiparticle mean free path. This enhancement is drastically suppressed in a very weak magnetic field. These results highlight that CeCoIn_5 is unique among superconductors. A small Fermi energy, a large superconducting gap, a short coherence length, and a long mean free path all indicate that CeCoIn_5 is clearly in the superclean regime (E_F/Delta<<l/xi), in which peculiar vortex state is expected.Comment: 5 pages, 5 figure