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Register a new userThermal and electromagnetic properties of Bi$_2$Sr$_2$CaCu$_2$O$_8$ intrinsic Josephson junction stacks studied via one-dimensional coupled sine-Gordon equations
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We used one-dimensional coupled sine-Gordon equations combined with heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a $300,mumathrm{m}$ long intrinsic Josephson junction stack consisting of $N = 700$ junctions. The junctions in the stack are combined to $M$ segments where we assume that inside a segment all junctions behave identically. Most simulations are for $M = 20$. For not too high bath temperatures there is the appearence of a hot spot at high bias currents. In terms of electromagnetic properties, robust standing wave patterns appear in the current density and electric field distributions. These patterns come together with vortex/antivortex lines across the stack that correspond to $pi$ kink states, discussed before in the literature for a homogeneous temperature distribution in the stack. We also discuss scaling of the thermal and electromagnetic properties with $M$, on the basis of simulations with $M$ between 10 and 350.
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We used 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a $250 times 70,mumathrm{m}^2$ intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power a hot spot forms in the stack. Resonant electromagnetic modes, oscillating either along the length ((0, $n$) modes) or the width (($m$, 0) modes) of the stack or having a more complex structure, can be excited both with and without a hot spot. At fixed bath temperature and bias current several cavity modes can coexist in the absence of a magnetic field. The (1, 0) mode, considered to be the most favorable mode for THz emission, can be stabilized by applying a small magnetic field along the length of the stack. A strong field-induced enhancement of the emission power is also found in experiment, for an applied field around 5.9 mT.
Low temperature thermal conductivity, $kappa$, of optimally-doped Bi2212 was studied before and after the introduction of point defects by electron irradiation. The amplitude of the linear component of $kappa$ remains unchanged, confirming the universal nature of heat transport by zero-energy quasiparticles. The induced decrease in the absolute value of $kappa$ at finite temperatures allows us to resolve a nonuniversal term in $kappa$ due to conduction by finite-energy quasiparticles. The magnitude of this term provides an estimate of the quasiparticle lifetime at subkelvin temperatures.
We report tunneling spectra of near optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ intrinsic Josephson junctions with area of 0.09 $mu$m$^2$, which avoid some fundamental difficulties in the previous tunneling experiments and allow a stable temperature-dependent measurement. A d-wave Eliashberg analysis shows that the spectrum at 4.2 K can be well fitted by considering electron couplings to a bosonic magnetic resonance mode and a broad high-energy continuum. Above $T_c$, the spectra show a clear pseudogap that persists up to 230 K, and a crossover can be seen indicating two different pseudogap phases existing above $T_c$. The intrinsic electron tunneling nature is discussed in the analysis.
In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level $p$. In most materials, $p$ cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, $T_mathrm{c}$, using the assumption that $T_mathrm{c}$ dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to $T_mathrm{c}=91$ K. We show that $p$ can be determined from the underlying Fermi surfaces and that $in-situ$ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of $2Delta_0=(4pm1)k_mathrm{B}T_mathrm{c}$
Tunneling spectra of near optimally doped, submicron Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ intrinsic Josephson junctions are presented, and examined in the region where the superconducting gap evolves into pseudogap. The spectra are analyzed using a self-energy model, proposed by Norman {it et al.}, in which both quasiparticle scattering rate $Gamma$ and pair decay rate $Gamma_{Delta}$ are considered. The density of states derived from the model has the familiar Dynes form with a simple replacement of $Gamma$ by $gamma_+$ = ($Gamma$ + $Gamma_{Delta}$)/2. The $gamma_+$ parameter obtained from fitting the experimental spectra shows a roughly linear temperature dependence, which puts a strong constraint on the relation between $Gamma$ and $Gamma_{Delta}$. We discuss and compare the Fermi arc behavior in the pseudogap phase from the tunneling and angle-resolved photoemission spectroscopy experiments. Our results indicate an excellent agreement between the two experiments, which is in favor of the precursor pairing view of the pseudogap.
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