Searcharxiv⌕ Search

arXiv subjects

T. Schneider

Publications and source records attributed to T. Schneider.

At least 55 records · Page 3Linked to original sources
arXiv2009

Study of leakage currents in pCVD diamonds as function of the magnetic field

pCVD diamond sensors are regularly used as beam loss monitors in accelerators by measuring the ionization of the lost particles. In the past these beam loss monitors showed sudden increases in the dark leakage current without beam losses and these erratic leakage currents were found to decrease, if magnetic fields were present. Here we report on a systematic study of leakage currents inside a magnetic field. The decrease of erratic currents in a magnetic field was confirmed. On the contrary, diamonds without erratic currents showed an increase of the leakage current in a magnetic field perpendicular to the electric field for fields up to 0.6T, for higher fields it decreases. A preliminary model is introduced to explain the observations.

physics.ins-det↗
arXiv2009

A tool to estimate the critical dynamics and thickness of superconducting films and interfaces

We demonstrate that the magnetic field dependence of the conductivity measured at the transition temperature allows the dynamical critical exponent, the thickness of thin superconducting films and interfaces, and the limiting lateral length to be determined. The resulting tool is applied to the conductivity data of an amorphous Nb0.15 Si0.85 film and a LaAlO3/SrTiO3 interface.

cond-mat.supr-con↗
arXiv2009

Evidence for Kosterlitz-Thouless and 3D-xy critical behavior in Bi2212

We present reversible magnetization data of a high quality Bi2212 single crystal and explore the occurrence of 3D-xy critical behavior close to the bulk transition temperature Tc and of Kosterlitz-Thouless (KT) behavior. Below and above the presumed Kosterlitz-Thouless transition temperature T_KT we observe the characteristic 2D-xy behavior: a downward shift of the crossing point phenomenon towards T_KT as the field is decreased and sufficiently below T_KT the characteristic 2D-xy relationship between the magnetization an the in-plane magnetic penetration depth. In contrast, the measured temperature dependence of the superfluid density does not exhibit the characteristic KT-behavior around the presumed T_KT. The absence of this feature is traced back to the 2D- to 3D-xy crossover setting in around and above T_KT. Invoking the Maxwell relation the anomalous field dependence of the specific heat peak is also traced back to the intermediate 2D-xy behavior. However, close to Tc we observe consistency with 3D-xy critical behavior, in agreement with measurements of the in-plane magnetic penetration depth.

cond-mat.supr-con↗
arXiv2009

Electrostatically tuned quantum superconductor-metal-insulator transition at the LaAlO3/SrTiO3 interface

Recently superconductivity at the interface between the insulators LaAlO3 and SrTiO3 has been tuned with the electric field effect to an unprecedented range of transition temperatures. Here we perform a detailed finite size scaling analysis to explore the compatibility of the phase transition line with Berezinskii-Kosterlitz-Thouless (BKT) behavior and a 2D-quantum phase(QP)-transition. In an intermediate regime, limited by a gate voltage dependent limiting length, we uncover remarkable consistency with a BKT-critical line ending at a metallic quantum critical point, separating a weakly localized insulator from the superconducting phase. Our estimates for the critical exponents of the 2D-QP-transition, z=1 and nu=0.66, suggest that it belongs to the 3D-xy universality class.

cond-mat.supr-con↗
arXiv2009

An EOM-assisted wave-vector-resolving Brillouin light scattering setup

Brillouin light scattering spectroscopy is a powerful technique which incorporates several extensions such as space-, time-, phase- and wave-vector resolution. Here, we report on the improvement of the wave-vector resolution by including an electro-optical modulator. This provides a reference to calibrate the position of the diaphragm hole which is used for wave-vector selection. The accuracy of this calibration is only limited by the accuracy of the wave-vector measurement itself. To demonstrate the validity of the approach the wave vectors of dipole-dominated spin waves excited by a microstrip antenna were measured.

cond-mat.other↗
arXiv2009

Phase sensitive Brillouin scattering measurements with a novel magneto-optic modulator

A recently reported phase sensitive Brillouin light scattering technique is improved by use of a magnetic modulator. This modulator is based on Brillouin light scattering in a thin ferrite film. Using this magnetic modulator in time- and space Brillouin light scattering measurements we have increased phase contrast and excluded influence of optical inhomogeneities in the sample. We also demonstrate that the quality of the resulting interference patterns can be improved by data postprocessing using the simultaneously recorded information about the reference light.

cond-mat.other↗
arXiv2009

Probing superconductivity in MgB2 confined to magnetic field tuned cylinders by means of critical fluctuations

We report and analyze reversible magnetization measurements on a high quality MgB2 single crystal in the vicinity of the zero field transition temperature, T_c=38.83 K, at several magnetic fields up to 300 Oe, applied along the c-axis. Though MgB2 is a two gap superconductor our scaling analysis uncovers remarkable consistency with 3D-xy critical behavior, revealing that close to criticality the order parameter is a single complex scalar as in 4He. This opens up the window onto the exploration of the magnetic field induced finite size effect, whereupon the correlation length transverse to the applied magnetic field H_i applied along the i-axis cannot grow beyond the limiting magnetic length L_Hi, related to the average distance between vortex lines. We find unambiguous evidence for this finite size effect. It implies that in type II superconductors, such as MgB2, there is the 3D to 1D crossover line H_pi and xi denotes the critical amplitudes of the correlation lengths above and below T_c along the respective axis. Consequently, above H_pi(T) and T<T_c superconductivity is confined to cylinders with diameter L_Hi (1D). In contrast, above T_c the uncondensed pairs are confined to cylinders. Accordingly, there is no continuous phase transition in the (H,T)-plane along the H_c2-lines as predicted by the mean-field treatment.

cond-mat.supr-con↗
arXiv2008

3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover

We present reversible magnetization data of a YBa2Cu4O8 single crystal and analyze the evidence for 3D-xy critical behavior and a magnetic field induced 3D to 1D crossover. Remarkable consistency with these phenomena is observed in agreement with a magnetic field induced finite size effect, whereupon the correlation length transverse to the applied magnetic field cannot grow beyond the limiting magnetic length scale L_H. By applying the appropriate scaling form we obtain the zero-field critical temperature, the 3D to 1D crossover, the vortex melting line and the universal ratios of the related scaling variables. Accordingly there is no continuous phase transition in the (H,T)-plane along the H_c2-lines as predicted by the mean-field treatment.

cond-mat.supr-con↗
arXiv2008

Superconductor - Normal and Quantum Superconductor-Insulator Transition at the LaAlO3/SrTiO3Interface

Superconductivity at the interface between the insulators LaAlO3 and SrTiO3 has been tuned with the electric field effect. The data provide evidence for a two dimensional quantum superconductor to insulator (2D-QSI) transition. Here we explore the compatibility of this phase transition line with Berezinskii-Kosterlitz-Thouless (BKT) behavior and a 2D-QSI transition. In an intermediate regime, limited by a finite size effect, we uncover remarkable consistency with BKT- criticality, weak localization in the insulating state and non-Drude behavior in the normal state. Our estimates for the critical exponents of the 2D-QSI-transition, z =1 and nu=3, suggest that it belongs to the 3D-xy universality class.

cond-mat.supr-con↗
arXiv2008

Electric Field Control of the LaAlO$_{3}$/SrTiO$_{3}$ Interface Ground State

Interfaces between complex oxides are emerging as one of the most interesting playgrounds in condensed matter physics. In this special setting, in which translational symmetry is artificially broken, a variety of novel electronic phases can be promoted. Theoretical studies predict complex phase diagrams and suggest the key role of the carrier density in determining the systems ground states. A particularly fascinating system is the interface between the insulators LaAlO$_{3}$ and SrTiO$_{3}$, which displays conductivity with high mobility. Recently two possible ground states have been experimentally identified: a magnetic state and a two dimensional (2D) superconducting condensate. In this Letter we use the electric field effect to explore the phase diagram of the system. The electrostatic tuning of the carrier density allows an on/off switching of superconductivity and drives a quantum phase transition (QPT) between a 2D superconducting state and an insulating state (2D-QSI). Analyses of the magnetotransport properties in the insulating state are consistent with weak localisation and do not provide evidence for magnetism. The electric field control of superconductivity demonstrated here opens the way to the development of novel mesoscopic superconducting circuits

cond-mat.supr-con↗
arXiv2008

Phase reciprocity of spin-wave excitation by a microstrip antenna

Using space-, time- and phase-resolved Brillouin light scattering spectroscopy we investigate the difference in phase of the two counterpropagating spin waves excited by the same microwave microstrip transducer. These studies are performed both for backward volume magnetostatic waves and magnetostatic surface waves in an in-plane magnetized yttrium iron garnet film. The experiments show that for the backward volume magnetostatic spin waves (which are reciprocal and excited symmetrically in amplitude) there is a phase difference of $π$ associated with the excitation process and thus the phase symmetry is distorted. On the contrary, for the magnetostatic surface spin waves (which are non-reciprocal and unsymmetrical in amplitude) the phase symmetry is preserved (there is no phase difference between the two waves associated with the excitation). Theoretical analysis confirms this effect.

cond-mat.other↗
arXiv2007

Realization of XNOR and NAND spin-wave logic gates

We demonstrate the functionality of spin-wave logic XNOR and NAND gates based on a Mach-Zehnder type interferometer which has arms implemented as sections of ferrite film spin-wave waveguides. Logical input signals are applied to the gates by varying either the phase or the amplitude of the spin waves in the interferometer arms. This phase or amplitude variation is produced by Oersted fields of dc current pulses through conductors placed on the surface of the magnetic films.

cond-mat.other↗
arXiv2007

Magnetic field induced 3D to 1D crossover in Sr0:9La0:1CuO2

The effect of the magnetic field on the critical behavior of Sr0:9La0:1CuO2 is explored in terms of reversible magnetization data. As the correlation length transverse to the magnetic field Hi,applied along the i-axis, cannot grow beyond the limiting magnetic length LHi, related to the average distance between vortex lines, one expects a magnetic field induced finite size effect. Invoking the scaling theory of critical phenomena we provide clear evidence for this effect. It implies that in type II superconductors there is a 3D to 1D crossover line Hpi(T). Consequently, below Tc and above Hpi(T) uperconductivity is confined to cylinders with diameter LHi(1D). Accordingly, there is no continuous phase transition in the (H,T)-plane along the Hc2-lines as predicted by the mean-field treatment.

cond-mat.supr-con↗
arXiv2007

Resonant scattering of spin waves from a region of inhomogeneous magnetic field in a ferromagnetic film

The transmission of a dipole-dominated spin wave in a ferromagnetic film through a localised inhomogeneity in the form of a magnetic field produced by a dc current through a wire placed on the film surface was studied experimentally and theoretically. It was shown that the amplitude and phase of the transmitted wave can be simultaneously affected by the current induced field, a feature that will be relevant for logic based on spin wave transport. The direction of the current creates either a barrier or well for spin wave transmission. The main observation is that the current dependence of the amplitude of the spin wave transmitted through the well inhomogeneity is non-monotonic. The dependence has a minimum and an additional maximum. A theory was constructed to clarify the nature of the maximum. It shows that the transmission of spin waves through the inhomogeneity can be considered as a scattering process and that the additional maximum is a scattering resonance.

cond-mat.mtrl-sci↗
arXiv2007

Quantum Superconductor-Metal Transition in Al, C doped MgB2 and overdoped Cuprates?

We consider the realistic case of a superconductor with a nonzero density of elastic scatterers, so that the normal state conductivity is finite. The quantum superconductor-metal (QSM) transition can then be tuned by varying either the attractive electron-electron interaction, the quenched disorder, or the applied magnetic field. We explore the consistency of the associated scaling relations, Tc ~ 1/lamda(0) ~ gap(0) ~ 1/gsi(0) ~ Hc2(0)^-0.5 and Tc(H) ~ 1/Lamda(0,H) ~ gap(0,h) ~ (Hc2(0)-H)^ 1/2, valid for all dimensions D > 2, with experimental data, in Al, C doped MgB2 and overdoped cuprates.

cond-mat.supr-con↗
arXiv2007

On the occurrence of Berezinskii-Kosterlitz-Thouless behavior in highly anisotropic cuprate superconductors

The conflicting observations in the highly anisotropic Bi2Sr2CaCu2O8+x, vidence for BKT behavior emerging from magnetization data and smeared 3D-xy behavior, stemming form the temperature dependence of the magnetic in-plane penetration depth are traced back to the rather small ratio, gsic+/gsic-=0.45, between the c-axis correlation length probed above (+) and below (-) Tc, and the comparatively large anisotropy. The latter leads to critical amplitudes gsic0+,-which are substantially smaller than the distance between two CuO2 double layers. In combination with gsic+/gsic-=0.45 and in contrast to the situation below Tc the c-axis correlation length gsic exceeds the distance between two CuO2 double layers very close to Tc only. Below this narrow temperature regime where 3D-xy fluctuations dominate, there is then an extended temperature regime where the units with two CuO2 double layers are nearly uncoupled so that 2D thermal fluctuations dominate and BKT features are observable.

cond-mat.supr-con↗
arXiv2006

Evidence for 3D-xy critical properties in underdoped YBa2Cu3O7+x

We perform a detailed analysis of the irreversible magnetization data of Salem-Sugui et al. and Babis et al. of underdoped and optimally doped YBa2Cu3O7+x single crystals. Near the zero field transition temperature we observe extended consistency with the properties of the 3D-xy universality class, even though the attained critical regime is limited by an inhomogeneity induced finite size effect. Nevertheless, as Tc falls from 93.5 to 41.5 K the critical amplitude of the in-plane correlation length gsiab0, the anisotropy amma=gsiab0/gsic0 and the critical amplitude of the in-plane penetration depth Lamdaab0 increase substantially, while the critical amplitude of the c-axis correlation length gsic0 does not change much. As a consequence, the correlation volume Vcorr increases and the ritical amplitude of the specific heat singularity A decreases dramatically, while the rise of gsiab0 reflects the behavior of the zero temperature counterpart. Conversely, although gsiab0 and lamdaab0 increase with reduced Tc, the Ginzburg-Landau parameter decreases substantially and YBa2Cu3O7+x crosses over from an extreme to a weak type-II superconductor.

cond-mat.supr-con↗