Apparent absence of Pauli paramagnetism in metallic polyparaphenylene

The magnetic susceptibility of doped and undoped polyparaphenylene has been measured in the temperature range from 5 to 300 K by the static Faraday method and by ESR. In the static experiments, a Curielike paramagnetism has been observed superimposed on a temperature-independent diamagnetic susceptibility. The Pauli paramagnetism of the doped samples is surprisingly small. Its upper limit has been determined to be only 2?10^?7 emu cm³/mole-carbon. —The concentration of magnetic centers in the doped samples is several orders of magnitude smaller than the dopant concentration and does not scale with it. — These results indicate a conduction mechanism involving nearly complete spin compensation of the charge carriers.     

Effects of spin paramagnetism on the magnetic field behavior of thin superconducting beryllium films

Tunneling measurements on thin superconducting Be in a parallel magnetic field show splitting of the quasiparticle states and other effects of Pauli paramagnetism with small spin-orbit scattering.     

Metastability and paramagnetism in superconducting mesoscopic disks

A projected order parameter is used to calculate not only local minima of the Ginzburg-Landau energy functional but also saddle points or energy barriers responsible for the metastabilities observed in superconducting mesoscopic disks [A. K. Geim et al., Nature (London) 396, 144 (1998)]. We calculate the local minima magnetization and find the energetic instability points between vortex configurations with different vorticity. We also find that, for any vorticity, the supercurrent can reverse its flow direction on decreasing the magnetic field before one vortex can escape.     

Pauli spin paramagnetism in amorphous Fe24Zr76

Results of the magnetic susceptibility, χ, measurements on amorphous Fe₂₄Zr₇₆ presented here when combined with the previously reported photoemission data enable us not only to separate unambiguously the Pauli spin and orbital contributions to χ but also to arrive at a reliable value for the Van Vleck susceptibility of pure Zr.     

Pauli paramagnetism and Landau level crossing in a modulation doped CdMnTe/CdMgTe quantum well

Electrical transport measurements are reported on a 2DEG in a CdMnTe quantum well structure. The amplitude of the Shubnikov-de Haas oscillations show a distinct beating pattern with nodes corresponding to coincidences between the spin splitting and a half integer multiple of the cyclotron energy. The observed pattern of nodes is a direct consequence of the large Pauli paramagnetism induced by the s-d exchange interaction between the spins of electronic states and the localized magnetic moments.     

Gauge fluctuations in superconducting films

In this paper we consider a type-I superconducting film modeled by the Ginzburg-Landau model, confined between two parallel planes a distance L apart from one another. Our approach is based on the Gaussian effective potential in the transverse unitarity gauge, which allows to treat gauge contributions in a compact form. Using techniques from dimensional and -function regularizations, modified by the confinement conditions, we investigate the critical temperature as a function of the film thickness L. The contributions from the scalar self-interaction and from the gauge fluctuations are clearly identified. The model suggests the existence of a minimal critical thickness below which superconductivity is suppressed. A comparison with present experimental observations is done.Received: 19 December 2003, Published online: 9 April 2004PACS: 74.20.-z Theories and models of superconducting state - 11.15.Ex Spontaneous breaking of gauge symmetries - 05.10.Cc Renormalization group methods     

Effect of interconfigurational fluctuations on superconducting magnetic alloys

A theory which includes impurity-atom correlation and many electron structure at the outset and gives rise to interconfigurational excitation energy resonances close to the Fermi energy is applied to effects of Ce impurities on the superconducting transition temperature of La and La_1?xTh_x, as functions of pressure and x respectively, and on the normal state resistivity of La as a function of pressure.     

Pauli paramagnetic effects on vortices in superconducting TmNi2B2C

The magnetic field distribution around the vortices in TmNi2B2C in the paramagnetic phase was studied experimentally as well as theoretically. The vortex form factor, measured by small-angle neutron scattering, is found to be field independent up to 0.6Hc2 followed by a sharp decrease at higher fields. The data are fitted well by solutions to the Eilenberger equations when paramagnetic effects due to the exchange interaction with the localized 4f Tm moments are included. The induced paramagnetic moments around the vortex cores act to maintain the field contrast probed by the form factor.     

Localized spin fluctuations in superconducting alloys

The effects due to localized spin fluctuations (LSF) in dilute superconducting alloys are investigated. Expressions for the critical temperature T_c as function of impurity concentration n_I and the specific heat jump at the transition ΔC(T_c) are obtained, both in the weak and strong magnetic limits. The results are discussed in the light of available experimental data.     

自旋涨落与非常规超导配对

铜氧化物高温超导、铁基高温超导、重费米子超导和κ-型层状有机超导等超导体的超导态都与磁性有序态相邻,且超导能隙在动量空间一般存在变号.因此,这些超导体的超导机理被认为有别于常规BCS超导中的电子交换声子导致的各向同性s-波配对.在这些非常规超导中,自旋涨落被认为是导致电子形成库珀对的主要起源之一.本文主要以铜基和铁基高...     

Critical fluctuations in a mesoscopic superconducting ring

The nonlocal magnetoconductivity fluctuations in a superconducting submicron ring, with radius comparable to the Ginzburg-Landau coherence length, are studied. The order parameter mode separation yields to the solution of the time-dependent Ginzburg-Landau equation and the paraconductivity Fourier components are calculated in the vicinity of the critical temperature, including the critical fluctuation region. The homogeneous component has a logarithmic singularity at T(c) while the other components are found to be not singular.     

Particle-hole mixing driven by the superconducting fluctuations

Development of the STM and ARPES spectroscopy enabled to reach the resolution sufficient for probing the particle-hole entanglement in superconducting materials, even above the critical temperature T_c. On a quantitative level one can characterize such entanglement in terms of the Bogoliubov angle which determines to what extent the particles and holes constitute the effective quasiparticles. In classical superconductors, where the phase transition is related to formation of the Cooper pairs almost simultaneously accompanied by onset of their long-range phase coherence, the Bogoliubov angle is slanted (due to finite particle-hole mixing) all the way up to T_c. In the high temperature superconductors and in superfluid ultracold fermion atoms near the Feshbach resonance the situation is different because the preformed pairs can exist above T_c albeit loosing coherence due to the strong quantum fluctuations. We discuss a generic temperature dependence of the Bogoliubov angle in such pseudogap state indicating a novel, non-BCS behavior. For analysis we use the two-component model describing the pairs coexisting with single fermions and study selfconsistently their feedback effects by the similarity transformation originating from the renormalization group approach.     

On the density fluctuations of the superconducting state

The fluctuations of the number of particles in a subvolumeΩ′≦Ω in the superconducting state are investigated in the framework of the strong coupling limit of the BCS-theory. It is shown for values ofΩ′?Ω these fluctuations are proportional to the subvolumeΩ′ and agree for theseΩ′-values with the density fluctuations of the quasivacuum state.     

高温超导体中的赝隙与超导位相涨落

高温超导体赝隙态与超导态之间的关系一直是研究的焦点.交流电导和能斯特（Nernst）效应测量相继探测到超导转变温度Tc0以上温区一定范围内存在磁通涡旋激发,利用力矩技术的磁化率测量则探测到超导涨落引起的弱抗磁性.这些发现都支持了高温超导体赝隙相中存在有限的超导序参量振幅和强烈的位相涨落的图像,说明Tc0处的相变是由库珀对之间长程位相关联的消失所驱动的.文章首先简短地介绍高温超导体的电子态相图和赝隙态,以及能斯特效应的原理和测量方法,然后对能斯特效应的测量结果作一评述性介绍,还讨论了相关的理论模型.