Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCharacterization of Shapiro steps in the presence of a 4{pi}-periodic Josephson current
85
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The Majorana zero-energy modes (MZMs) residing at the boundary of topological superconductors have attracted a great deal of interest recently, as they provide a platform to explore fundamental physics such as non-Abelian statistics, as well as fault-tolerant quantum computation. Period doubling of Shapiro steps in a Josephson junction under microwave irradiation has been regarded as strong evidence for the emergence of the MZMs at the junction edges. However, questions remain as to how the Shapiro steps respond to the presence of a 4{pi}-periodic Josephson current. In this study, we investigated the characteristic features of Shapiro steps with respect to the ratio ({alpha}) of the 4{pi}-periodic current to the topologically trivial 2{pi}-periodic one, as well as the reduced microwave frequency ({Omega}) and McCumber parameter ({beta}) of the junction. Our analysis reproduced Shapiro steps similar to those observed experimentally for specific parameter sets of {alpha},{Omega} ({lesssim 0.1}), and {beta} ({gtrsim 1.0}). Full suppression of the first lobe of the n=1 step guarantees the presence of a 4{pi}-periodic Josephson current.In addition, we discuss the range of {Omega} and {beta} needed for full suppression of the first lobe of the {n=1} step, even for small {alpha} ({<0.1}). To observe period-doubled Shapiro steps, even with a small {alpha}, the junction should have a large {I_c}{R_N} product and sufficiently large junction capacitance.
rate research
Read More
A superconducting quantum interference device (SQUID) comprising 0- and $pi$-Josephson junctions (JJs), called $pi$-SQUID, is studied by the resistively shunted junction model. The $pi$-SQUID shows half-integer Shapiro-steps (SS) under microwave irradiation at the voltage $V$ = $(hbar/2e)Omega (n/2)$, with angular frequency $Omega$ and half-integer $n$/2 in addition to integer $n$. We show that the $pi$-SQUID can be a $pi$-qubit with spontaneous loop currents by which the half-integer SS are induced. Making the 0- and $pi$-JJs equivalent is a key for the half-integer SS and realizing the $pi$-qubit.
We investigate the current-phase relation of S/F/S junctions near the crossover between the 0 and the pi ground states. We use Nb/CuNi/Nb junctions where this crossover is driven both by thickness and temperature. For a certain thickness a non-zero minimum of critical current is observed at the crossover temperature. We analyze this residual supercurrent by applying a high frequency excitation and observe the formation of half-integer Shapiro steps. We attribute these fractional steps to a doubling of the Josephson frequency due to a sin(2*phi) current-phase relation. This phase dependence is explained by the splitting of the energy levels in the ferromagnetic exchange field.
We treat theoretically Shapiro steps in tunnel Josephson junctions with spatially alternating critical current density. Explicit analytical formulas for the width of the first integer (normal) and half-integer (anomalous) Shapiro steps are derived for short junctions. We develop coarse-graining approach, which describes Shapiro steps in the voltage-current curves of the asymmetric grain boundaries in YBCO thin films and different superconductor-ferromagnet-superconductor Josephson-type heterostructures.
We present measurements of the current-phase relation (CPR) of Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions as a function of temperature. The CPR is determined by incorporating the junction into a superconducting loop coupled to a dc SQUID, allowing measurement of the junction phase difference. Junctions fabricated with a thin (~ 22 nm) barrier of Cu0.47Ni0.53 sandwiched between Nb electrodes exhibit a re-entrant critical current with temperature, vanishing at T =T_pi ~ 2-4 K. We find that the critical current is negative for T < T_pi, indicating that the junction is a pi-Josephson junction. We find no evidence for second-order Josephson tunneling near T_pi in the CPR predicted by several theories.
We propose a scheme to detect the Majorana bound states (MBSs) by a thermodynamically stable D.C. Josephson current with $4pi$-periodicity in the superconducting phase difference, which is distinct from the previous A.C. $4pi$-periodicity found in topological superconducting Josephson junctions. The scheme, consisting of a quantum dot coupled to two s-wave superconducting leads and a floating topological superconductor supporting two MBSs at its ends, only exploits the interplay of a local Zeeman field and the exotic helical and self-Hermitian properties of MBSs, without requiring the conservation of fermion parity and not relying on the zero-energy property of MBSs. Our D.C. $4pi$-periodicity is thus robust against the overlap between the two MBSs and various system parameters, including the local Coulomb interaction, the tunneling asymmetry, and the width of superconducting gap, which facilitates experimentally detection of the MBSs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
