We report specific heat measurements of the heavy fermion superconductor CeCoIn5 in the vicinity of the superconducting critical field Hc2, with magnetic field in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first order for field above 10 T for H [110] and H [100]. In the same range of magnetic field we observe a second specific heat anomaly within the superconducting state. We interpret this anomaly as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) One is the interaction of the spin of the electron with magnetic field and the other is the energy of the superconducting coupling of electrons into Cooper pairs, or the condensation energy. In the normal state the electrons are free to lower their total energy by preferentially aligning their spins along the magnetic field, leading to a temperature-independent Pauli susceptibility. For spinsinglet superconductors (both s-and d-wave), the condensate contains an equal number of spin-up and spindown electrons. Therefore, Pauli paramagnetism will always favor the normal state over the spin-singlet superconducting state, and will reduce the superconducting critical field H c2 which suppresses superconductivity. This effect is called Pauli limiting, with the characteristic Pauli field H P determining the upper bound of H c2 [3]. Another effect of magnetic field that leads to the suppression of superconductivity is orbital limiting, or suppression of superconductivity when the kinetic energy of the supercurrent around the normal cores of the superconducting vortices in Type II superconductors becomes greater than the superconducting condensation energy. The orbital limiting field H A number of conventional superconductors were proposed as candidates for observation of the FFLO state, due to their high orbital critical field H c20 and, therefore, relatively strong Pauli limiting effect, in the early and mid-sixties. Experimental searches, however, yielded null results [5,6,7,8]. The failure to observe the FFLO state was attributed to high spin-orbit scattering rate in these compounds [9]. In the last decade the FFLO state was suggested to exist in heavy fermion UPd 2 Al 3 (Ref. [10] and CeRu 2 (Ref.[11]), based on thermal expansion and magnetization data, respectively. Subsequent research identified the magnetization feature in CeRu 2 as due to flux motion [12], and the region of the suggested FFLO state in UPd 2 Al 3 was shown to be inconsistent with theoretical models [13]. Most notably, multiple phase transitions that can be associated with the FFLO state have not been observed with a single measurement technique.Heavy-fermion superconductor CeCoIn 5 satisfies all requirements of theory for the formation of the FFLO state. It is very clean, with an electronic mean free path on the order of microns in the superconducting state, which significantly exceeds the superconducting correlation length [14]. Its Maki parameter α ≈ 3.5 is twice the minimum required for the format...

Bismuth vanadate (BiVO4) is a promising photoelectrode material for the oxidation of water, but fundamental studies of this material are lacking. To address this, we report electrical and photoelectrochemical (PEC) properties of BiVO4 single crystals (undoped, 0.6% Mo, and 0.3% W:BiVO4) grown using the floating zone technique. We demonstrate that a small polaron hopping conduction mechanism dominates from 250 to 400 K, undergoing a transition to a variable-range hopping mechanism at lower temperatures. An anisotropy ratio of ~3 was observed along the c axis, attributed to the layered structure of BiVO4. Measurements of the ac field Hall effect yielded an electron mobility of ~0.2 cm(2) V(-1) s(-1) for Mo and W:BiVO4 at 300 K. By application of the Gärtner model, a hole diffusion length of ~100 nm was estimated. As a result of low carrier mobility, attempts to measure the dc Hall effect were unsuccessful. Analyses of the Raman spectra showed that Mo and W substituted for V and acted as donor impurities. Mott-Schottky analysis of electrodes with the (001) face exposed yielded a flat band potential of 0.03-0.08 V versus the reversible H2 electrode, while incident photon conversion efficiency tests showed that the dark coloration of the doped single crystals did not result in additional photocurrent. Comparison of these intrinsic properties to those of other metal oxides for PEC applications gives valuable insight into this material as a photoanode.

We present a study of Nernst effect in underdoped La(2-x)Sr(x)CuO4 in magnetic fields as high as 28 T. At high fields, a sizable Nernst signal was found to persist in the presence of a field-induced nonmetallic resistivity. By simultaneously measuring resistivity and the Nernst coefficient, we extract the entropy of vortex cores in the vicinity of this field-induced superconductor-insulator transition. Moreover, the temperature dependence of the thermoelectric Hall angle provides strong constraints on the possible origins of the finite Nernst signal above T(c), as recently discovered by Xu et al. [Nature (London) 406, 486 (2000)].

We report a systematic study of high magnetic field specific heat and resistivity in single crystals of CeCoIn5 for the field oriented in the basal plane (H ab) of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T 2 law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H c), the emergent picture is that of a magnetic field tuned quantum critical point which exists in the vicinity of the superconducting H 0 c2 despite a variation of a factor of 2.4 in H 0 c2 for different field orientations. This suggests an underlying physical reason exists for the superconducting H 0 c2 to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi Liquid ground state with increasing magnetic field is more gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in-plane. Together with the close proximity of the quantum critical point and H 0 c2 in CeCoIn5 for both field orientation, the anisotropy in the recovery of the Fermi liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical. PACS numbers:Quantum critical points mark the change in the ground state of a strongly correlated electron system, and the associated quantum fluctuations have tremendous consequences for the properties of the system at finite temperatures. Attention has focused on the heavy fermion superconductor CeCoIn 5 in the context of quantum criticality since its discovery [1]. Superconductivity in this material is not only unconventional (probably d-wave [2, 3]) and Pauli-limited (with the possible presence of a Fulde-Ferrell-Larkin-Ovchinnikov state at low temperatures) [4,5,6] but it is also built out of a normal state displaying Non Fermi Liquid behavior. Indeed, the normal state is characterized by a resistivity almost linear in temperature for a decade above T c in zero field [1], a specific heat coefficient diverging logarithmically over a large temperature range with a similar slope at zero and finite magnetic field [1,7], and a power law behavior in ac-susceptibility [1,7] and the nuclear spin-lattice relaxation rate [8]. All of this suggests the proximity to an antiferromagnetic instability. It is important to note that the specific heat is analogous to UBe 13 [9]. Since the entropy is conserved between the zero field superconducting state and the anomalous normal state at H 0 c2 , this implies that the mass enhancement leading to the heavy fermion ground state is interrupted by the formation of superconductivity and presumably the same spin fluctuations are responsible for both phenomena.The phase diagram of CeCoIn 5 turns out to be rather complex, raising the possibility of one or more quantum critical...