Extremely high upper critical magnetic field of the noncentrosymmetric heavy fermion superconductor CeRhSi3

We report an extremely high upper critical field B(c2) in the noncentrosymmetric heavy fermion superconductor CeRhSi3 for a magnetic field B along the tetragonal c axis. B(c2)(T=0) possibly reaching 30 T is much higher than B(c2)(0)=7 T for B perpendicular c and greatly exceeds the paramagnetic limiting field. The strong anisotropy of B(c2)(0) with extremely high B(c2)(0) for B || c is qualitatively explained by the paramagnetic pair-breaking mechanism specific to the noncentrosymmetric superconductor. However, an unusual B(c2)(T) curve with a positive curvature for B || c cannot be explained satisfactorily by conventional orbital pair-breaking models.     

Enhancement of the quantum-liquid phase by increased resistivity in thick a-MoxSi1-x films

Effects of normal-state resistivity rho(n) on the vortex phase diagram at low temperature T have been studied based on dc and ac complex resistivities for thick amorphous MoxSi(1-x) films. It is commonly observed irrespective of rho(n) that, in the limit T=0, the vortex-glass-transition line B(g)(T) is independent of T and extrapolates to a field below the T=0 upper critical field B(c2)(0), indicative of the quantum-vortex-liquid (QVL) phase in the regime B(g)(0)相似文献   

Towards the identification of a quantum critical line in the (p, B) phase diagram of CeCoIn5 with thermal-expansion measurements

The low-temperature thermal expansion of CeCoIn(5) single crystals measured parallel and perpendicular to magnetic fields B oriented along the c axis yields the volume thermal-expansion coefficient β. Considerable deviations of β(T) from Fermi-liquid behavior occur already within the superconducting region of the (B, T) phase diagram and become maximal at the upper critical field B(c2)(0). However, β(T) and the Grüneisen parameter Γ are incompatible with a quantum critical point at B(c2)(0), but allow for a quantum criticality shielded by superconductivity and extending to negative pressures for B相似文献   

Size effects under a strong magnetic field: Hall effect induced by electron-surface scattering on thin gold films deposited onto mica substrates under high vacuum

We report measurements of the Hall effect performed on 4 gold films evaporated onto mica substrates where the signal arises primarily from electron-surface scattering. The measurements were performed at low temperatures T (4 K < or = T < or = 50 K) under high magnetic field strengths B (1.5 T < or = B < or = 9 T), with B oriented perpendicular to the films.     

Anisotropy of the Sommerfeld coefficient in magnesium diboride single crystals

The anisotropic field dependence of the Sommerfeld coefficient gamma has been measured down to B-->0 by combining specific heat and Hall probe magnetization measurements in MgB2 single crystals. We find that gamma(B,theta) is the sum of two contributions arising from the sigma and pi band, respectively. We show that gammasigma(B,theta)=B/Bc2(theta) where Bc2(theta)=Bc2ab/sqrt[sin2theta+Gamma2cos2theta] with Gamma approximately 5.4 (theta being the angle between the applied field and the c axis) and gammapi(B,theta)=gammapi(B)=B/Bpi(B). The "critical field" of the pi band Bpi is fully isotropic but field dependent increasing from approximately 0.25 T for B< or =0.1 T up to 3 T approximately Bc2c for B-->3 T. Because of the coupling of the two bands, superconductivity survives in the pi band up to 3 T but is totally destroyed above for any orientation of the field.     

Observation of magnetic level repulsion in Fe6:Li molecular antiferromagnetic rings

Heat capacity (C), magnetic torque, and proton NMR relaxation rate (1/T(1)) measurements were performed on Fe6:Li single crystals in order to study the crossings between S = 0 and S = 1 and between S = 1 and S = 2 magnetic states of the molecular rings, at magnetic fields B(c1) = 11.7 T and B(c2) = 22.4 T, respectively. C vs B data at 0.78 K show that the energy gap between two states remains finite at B(c)'s (Delta(1)/k(B) = 0.86 K and Delta(2)/k(B) = 2.36 K) thus proving that levels repel each other. The large Delta(1) value may also explain the anomalously large width of the peak in 1/T(1) vs B, around B(c1). This anticrossing, unexpected in a centrosymmetric system, requires a revision of the Hamiltonian.     

Determination of blood longitudinal relaxation time (T1) at high magnetic field strengths

In this study, a circulation system was used to measure T(1) values of bovine blood under physiological conditions at field strengths of 4.7, 7 and 9.4 T. Results show that T(1) increases linearly with magnetic field B(0) and can be described with the equation T(1)=129 ms/T B(0)+1167 ms for magnetic field strengths between 1.5 and 9.4 T.     

Anisotropy and magnetic field effects on the entanglement of a two qubit Heisenberg XY chain

We investigate the entanglement of a two-qubit anisotropic Heisenberg XY chain in thermal equilibrium at temperature T in the presence of an external magnetic field B along the z axis. By means of the combined influences of anisotropic interactions and a magnetic field B, one is able to produce entanglement for any finite T, by adjusting the magnetic field strength. This contrasts with the isotropic interaction or the B = 0 cases, for which there is no entanglement above a critical temperature T(c) that is independent of the external B field.     

Measurement of the B(+) production cross section in pp collisions at sqrt[s]=7 TeV

Measurements of the total and differential cross sections dσ/dp(T)(B) and dσ/dy(B) for B(+) mesons produced in pp collisions at sqrt[s]=7 TeV are presented. The data correspond to an integrated luminosity of 5.8 pb(-1) collected by the CMS experiment operating at the LHC. The exclusive decay B(+)→J/ψK(+), with J/ψ→μ(+)μ(-), is used to detect B(+) mesons and to measure the production cross section as a function of p(T)(B) and y(B). The total cross section for p(T)(B)>5 GeV and |y(B)|<2.4 is measured to be 28.1±2.4±2.0±3.1 μb, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement.     

D-wave specific heat in Y-123 and Bi-2212 single crystals: new data,alternative explanation

The low temperature specific heat of Bi-2212 and Y-123 is measured for 1.2≤T≤7K and 0≤B≤14 T. We find that the field-induced “linear” term λ^*(B)?λ^*(0) near 1–3K saturates for B≥8 T, decreases as a function of temeprature, and has nearly the same amplitude for both compounds. This is not easily reconciled with the predicted d-wave contribution C∝γT(B/B_c2)^1/2. Oscillations of 2D vortices offer an alternative explanation.     

T1rho-weighted MRI using a surface coil to transmit spin-lock pulses

T1rho-weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B1 inhomogeneity. First, excitation with a spatially varying B1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B1 results in non-uniform T1rho contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T1rho-weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This "self-compensating" T1rho-preparatory pulse sequence was analyzed and the effect of an inhomogeneous B1 field was simulated using the Bloch equations. T1rho-weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T1rho-prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse.     

T1ρ-weighted MRI using a surface coil to transmit spin-lock pulses

T1rho-weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B1 inhomogeneity. First, excitation with a spatially varying B1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B1 results in non-uniform T1rho contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T1rho-weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This "self-compensating" T1rho-preparatory pulse sequence was analyzed and the effect of an inhomogeneous B1 field was simulated using the Bloch equations. T1rho-weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T1rho-prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse.     

Field dependence of the muon spin relaxation rate in MnSi

Muon spin rotation/relaxation measurements have been performed in the itinerant helical magnet MnSi at ambient pressure and at 8.3 kbar. We have found the following: (a) the spin-lattice relaxation rate 1/T(1) shows divergence as T1T proportional, variant (T-T(c))(beta) with the power beta larger than 1 near T(c); (b) 1/T(1) is strongly reduced in an applied external field B(L) and the divergent behavior near T(c) is completely suppressed at B(L)> or =4000 G. We discuss that (a) is consistent with the self-consistent renormalization theory and reflects a departure from "mean-field" behavior, while (b) indicates selective suppression of spin fluctuations of the q=0 component by B(L).     

Nonequilibrium transport through a Kondo dot in a magnetic field: perturbation theory and poor man's scaling

We consider electron transport through a quantum dot described by the Kondo model in the regime of large transport voltage V in the presence of a magnetic field B with max((V,B)>T(K). The electric current I and the local magnetization M are found to be universal functions of V/T(K) and B/T(K), where T(K) is the equilibrium Kondo temperature. We present a generalization of the perturbative renormali-zation group to frequency dependent coupling functions, as necessitated by the structure of bare perturbation theory. We calculate I and M within a poor man's scaling approach and find excellent agreement with experiment.     

Low-temperature susceptibility of the noncentrosymmetric superconductor CePt3Si

We report ac susceptibility measurements of polycrystalline CePt(3)Si down to 60 mK and in applied fields up to 9 T. In a zero applied field, a full Meissner state emerges at temperatures T/T(c) < 0.3, where T(c) = 0.65 K is the onset transition temperature. Though transport measurements show a relatively high upper critical field B(c2) approximately 4-5 T, the low-temperature susceptibility chi(') is quite fragile to the applied field, with chi(') diminishing rapidly in fields of a few kG. Interestingly, the field dependence of chi(') is well described by the power law 4pichi(') + 1 = (B/B(c))(1/2), where B(c) is the field at which the onset of resistance is observed in transport measurements.     

Temperature and magnetic-field-enhanced hall slope of a dilute 2D hole system in the ballistic regime

We report the temperature (T) and perpendicular magnetic-field (B) dependence of the Hall resistivity rho(xy)(B) of dilute metallic 2D holes in GaAs over a broad range of temperature (0.02-1.25 K). The low B Hall coefficient, R(H), is found to be enhanced when T decreases. Strong magnetic fields further enhance the slope of rho(xy)(B) at all temperatures studied. Coulomb interaction corrections of a Fermi liquid (FL) in the ballistic regime can not explain the enhancement of rho(xy) which occurs in the same regime as the anomalous metallic longitudinal conductivity. In particular, although the metallic conductivity in 2D systems has been attributed to electron interactions in a FL, these same interactions should reduce, not enhance, the slope of rho(xy)(B) as T decreases and/or B increases.     

Ferromagnetic quantum critical fluctuations in YbRh2(Si0.95Ge0.05)2

The bulk magnetic susceptibility chi(T,B) of YbRh(2)(Si(0.95)Ge(0.05))(2) has been investigated close to the field-induced quantum critical point at B(c) = 0.027 T. For B < or= 0.05 T a Curie-Weiss law with a negative Weiss temperature is observed at temperatures below 0.3 K. Outside this region, the susceptibility indicates ferromagnetic quantum critical fluctuations, chi(T) proportional, variantT-0.6 above 0.3 K. At low temperatures the Pauli susceptibility follows chi(0) proportional, variant(B-B(c))(-0.6) and scales with the coefficient of the T(2) term in the electrical resistivity. The Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the critical field.     

Ferromagnetism Induced in UCoAl by Uniaxial Pressure

UCoAl exhibits attributes of an itinerant 5f-electron metamagnet. It is paramagnetic down to lowest temperatures but the c -axis susceptibility shows a maximum around T max , 20 K. When a field larger than B c , 0.6 T is applied along the c -axis of hexagonal structure a ferromagnetic ordering of U moments is induced at low temperatures. The critical parameters T max and B c are sensitive to alloying and hydrostatic pressure. In the latter case values of both, T max and B c , are increasing with increasing pressure, i.e. metamagnetism is suppressed towards a conventional paramagnetism. We report on results of an experiment with a c -axis uniaxial pressure, which has an opposite influence on T max and B c leading to ferromagnetism in zero field. A scenario of the physics of UCoAl is presented accounting for effects of hydrostatic- and uniaxial-pressure on the lattice and consequences in the 5f-electron delocalization and anisotropy of hybridization-mediated exchange interactions.     

Effects of a parallel magnetic field on the metal-insulator transition in a dilute two-dimensional electron system

The temperature dependence of conductivity sigma(T) of a two-dimensional electron system in silicon has been studied in parallel magnetic fields B. At B = 0, the system displays a metal-insulator transition at a critical electron density n(c)(0), and dsigma/dT>0 in the metallic phase. At low fields ( B < or approximately equal to 2 T), n(c) increases as n(c)(B)-n(c)(0) proportional, variant Bbeta ( beta approximately 1), and the zero-temperature conductivity scales as sigma(n(s),B,T = 0)/sigma(n(s),0,0) = f(B(beta)/delta(n)), where delta(n) = [n(s)-n(c)(0)]/n(c)(0) and n(s) is electron density, as expected for a quantum phase transition. The metallic phase persists in fields of up to 18 T, consistent with the saturation of n(c) at high fields.     

Magnetic hyperfine fields of vacancy-associated119Sn in ion-implanted nickel

Magnetic hyperfine fields of¹¹⁹Sn impurity defects in nickel have been investigated by Mössbauer emission spectroscopy. Radioactive¹¹⁹Xe isotopes were implanted, annealing was performed after¹¹⁹Xe had decayed to¹¹⁹Sb. At least five different components with well-defined magnetic hyperfine fields, isomer shifts and Debye temperatures are identified in the rather complex spectra. One of these (B=2T) is known to be due to substitutional Sn. The hyperfine fields of the other components are pronouncedly larger (B=9T, B=15T, and B=17T, respectively, for single crystals). These defects are proposed to be Sn-multivacancy defects.