arXiv subjects

P. W. Adams

Publications and source records attributed to P. W. Adams.

42 records · Page 3Linked to original sources

arXiv2003

High Magnetic Field Sensor Using LaSb2

The magnetotransport properties of single crystals of the highly anisotropic layered metal LaSb2 are reported in magnetic fields up to 45 T with fields oriented both parallel and perpendicular to the layers. Below 10 K the perpendicular magnetoresistance of LaSb2} becomes temperature independent and is characterized by a 100-fold linear increase in resistance between 0 and 45 T with no evidence of quantum oscillations down to 50 mK. The Hall resistivity is hole-like and gives a high field carrier density of n ~ 3x10^20 cm^-3. The feasibility of using LaSb2 for magnetic field sensors is discussed.

cond-mat.mtrl-sci↗

arXiv2003

Superconducting Properties of MgCNi3 Films

We report the magnetotransport properties of thin polycrystalline films of the recently discovered non-oxide perovskite superconductor MgCNi3. CNi3 precursor films were deposited onto sapphire substrates and subsequently exposed to Mg vapor at 700 C. We report transition temperatures (Tc) and critical field values (Hc2) of MgCNi3 films ranging in thickness from 7.5 nm to 100 nm. Films thicker than ~40 nm have a Tc ~ 8 K, and an upper critical field Hc2 ~ 14 T, which are both comparable to that of polycrystalline powders. Hall measurements in the normal state give a carrier density, n =-4.2 x 10^22 cm^-3, that is approximately 4 times that reported for bulk samples.

cond-mat.supr-con↗

arXiv2002

Field Suppression of the Density-of-States: A Mechanism for Large Linear Magnetoresistance

Hall, resistivity, magnetization, and thermoelectric power measurements were performed on single crystals of the highly anisotropic layered metal LaSb2. A 100-fold linear magnetoresistance (MR) was observed in fields up to 45 T, with no indication of saturation. We show that the MR is associated with a magnetic-field-dependent holelike carrier density, n(H) \propto 1/H. The effect is orbital, depending upon the component of the magnetic field normal to the layers. At low temperature, a field of 9 T reduces the carrier density by more than an order of magnitude.

cond-mat.mtrl-sci↗

arXiv2001

Structure and Superconducting Properties of "BeB_2"

We present the crystal structure and low temperature electronic transport properties of the intermetallic commonly known as BeB_2. In contrast to the much simpler AlB_2-type structure of the 39K superconductor MgB_2, BeB_2 forms a complex structure type that is nearly unique in nature. The structure has 110.5 atoms per unit cell and a stoichiometry BeB_{2.75}. Polycrystalline Be(^{10.8}B)_{2.75} is superconducting below T_c=0.72K with a critical magnetic field H_{c2}=0.175T. Isotopically pure ^{10.0}B samples of have an enhanced$T_c=0.79K, consistent with a BCS isotope effect. Hall effect measurements suggest that the material is intrinsically compensated.

cond-mat.supr-con↗

arXiv2000

Coulomb Gap: How a Metal Film Becomes an Insulator

Electron tunneling measurements of the density of states (DOS) in ultra-thin Be films reveal that a correlation gap mediates their insulating behavior. In films with sheet resistance $R<5000Ω$ the correlation singularity appears as the usual perturbative $ln(V)$ zero bias anomaly (ZBA) in the DOS. As R is increased further, however, the ZBA grows and begins to dominate the DOS spectrum. This evolution continues until a non-perturbative $|V|$ Efros-Shklovskii Coulomb gap spectrum finally emerges in the highest R films. Transport measurements of films which display this gap are well described by a universal variable range hopping law $R(T)=(h/2e^2)exp(T_o/T)^{1/2}$.

cond-mat.str-el↗

arXiv2000

Tenfold Magnetoconductance in a Non-Magnetic Metal Film

We present magnetoconductance (MC) measurements of homogeneously disordered Be films whose zero field sheet conductance (G) is described by the Efros-Shklovskii hopping law $G(T)=(2e^2/h)\exp{-(T_o/T)^{1/2}}$. The low field MC of the films is negative with G decreasing 200% below 1 T. In contrast the MC above 1 T is strongly positive. At 8 T, G increases 1000% in perpendicular field and 500% in parallel field. In the simpler parallel case, we observe {\em field enhanced} variable range hopping characterized by an attenuation of $T_o$ via the Zeeman interaction.

cond-mat.str-el↗