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Register a new userHiggs mode mediated enhancement of interlayer transport in high-$T_c$ cuprate superconductors
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We put forth a mechanism for enhancing the interlayer transport in cuprate superconductors, by optically driving plasmonic excitations along the $c$ axis with a frequency that is blue-detuned from the Higgs frequency. The plasmonic excitations induce a collective oscillation of the Higgs field which induces a parametric enhancement of the superconducting response, as we demonstrate with a minimal analytical model. Furthermore, we perform simulations of a particle-hole symmetric $U(1)$ lattice gauge theory and find good agreement with our analytical prediction. We map out the renormalization of the interlayer coupling as a function of the parameters of the optical field and demonstrate that the Higgs mode mediated enhancement can be larger than $50%$.
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Evidence from NMR of a two-component spin system in cuprate high-$T_c$ superconductors is shown to be paralleled by similar evidence from the electronic entropy so that a two-component quasiparticle fluid is implicated. We propose that this two-component scenario is restricted to the optimal and underdoped regimes and arises from the upper and lower branches of the reconstructed energy-momentum dispersion proposed by Yang, Rice and Zhang (YRZ) to describe the pseudogap. We calculate the spin susceptibility within the YRZ formalism and show that the doping and temperature dependence reproduces the experimental data for the cuprates.
The interplay between structural and electronic degrees of freedom in complex materials is the subject of extensive debate in physics and materials science. Particularly interesting questions pertain to the nature and extent of pre-transitional short-range order in diverse systems ranging from shape-memory alloys to unconventional superconductors, and how this microstructure affects macroscopic properties. Here we use neutron and X-ray scattering to uncover universal structural fluctuations in La$_{2-x}$Sr$_x$CuO$_4$ and Tl$_2$Ba$_2$CuO$_{6+{delta}}$, two cuprate superconductors with distinct point disorder effects and optimal superconducting transition temperatures. The fluctuations are present in wide doping and temperature ranges, including compositions that maintain high average structural symmetry, and they exhibit unusual, yet simple scaling laws. We relate this behavior to pre-transitional phenomena in a broad class of systems with martensitic transitions, and argue that it can be understood as a rare-region effect caused by intrinsic, doping- and compound-independent nanoscale inhomogeneity. We also uncover remarkable parallels with superconducting fluctuations, which indicates that the underlying inhomogeneity plays a pivotal role in cuprate physics.
We analyse fluctuations about $T_c$ in the specific heat of (Y,Ca)Ba$_2$Cu$_3$O$_{7-delta}$, YBa$_2$Cu$_4$O$_8$ and Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$. The mean-field transition temperature, $T_c^{mf}$, in the absence of fluctuations lies well above $T_c$ especially at low doping where it reaches as high as 150K. We show that phase and amplitude fluctuations set in simultaneously and $T_c^{mf}$ scales with the gap, $Delta_0$, such that $2Delta_0/k_BT_c^{mf}$ is comparable to the BCS weak-coupling value, 4.3, for d-wave superconductivity. We also show that $T_c^{mf}$ is unrelated to the pseudogap temperature, $T^*$.
From study of the Kosterlitz-Thouless-Berezinskii (KTB) transition in the superfluid density, n_s(T), of ultrathin c-axis oriented YBa_{2}Cu_{3}O_{7-delta} (YBCO) films, we find that interlayer coupling is unexpectedly strong. The KTB transition occurs at a high temperature, as if the films were isotropic rather than quasi-two-dimensional. This result agrees with a comparison of the superfluid density of YBCO with Bi_{2}Sr_{2}CaCu_{2}O_{8} and with numerical simulations of Josephson junction arrays, and challenges the thermal phase fluctuation interpretation of critical behavior near T_c in YBCO.
When a continuous symmetry of a physical system is spontaneously broken, two types of collective modes typically emerge: the amplitude and phase modes of the order-parameter fluctuation. For superconductors, the amplitude mode is recently referred to as the Higgs mode as it is a condensed-matter analogue of a Higgs boson in particle physics. Higgs mode is a scalar excitation of the order parameter, distinct from charge or spin fluctuations, and thus does not couple to electromagnetic fields linearly. This is why the Higgs mode in superconductors has evaded experimental observations over a half century after the initial theoretical prediction, except for a charge-density-wave coexisting system. With the advance of nonlinear and time-resolved terahertz spectroscopy techniques, however, it has become possible to study the Higgs mode through the nonlinear light-Higgs coupling. In this review, we overview recent progresses on the study of the Higgs mode in superconductors.
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