Superconducting Pb stripline resonators in parallel magnetic field and their application for microwave spectroscopy

Abstract

Abstract. Planar superconducting microwave resonators are key elements in a variety of technical applications and also act as sensitive probes for microwave spectroscopy of various materials of interest in present solid state research. Here superconducting Pb is a suitable material as a basis for microwave stripline resonators.To utilize Pb stripline resonators in a variable magnetic field (e.g. in ESR measurements), the electrodynamics of such resonators in finite magnetic field has to be well understood. Therefore we performed microwave transmission measurements (with ample applied power to work in linear response) on superconducting Pb stripline resonators in a variable, parallel magnetic field. We determined surface resistance, penetration depth as well as real and imaginary parts, σ 1 and σ 2 , of the complex conductivity of superconducting Pb as a function of magnetic field. Here we find features reminiscent of those in temperaturedependent measurements, such as a maximum in σ 1 (coherence peak). At magnetic fields above the critical field of this type-I superconductor we still find a low-loss microwave response, which we assign to remaining superconductivity in the form of filaments within the Pb. Hysteresis effects are found in the quality factor of resonances once the swept magnetic field has exceeded the critical magnetic field. This is due to normal conducting areas that are pinned and can therefore persist in the superconducting phase. Besides zero-field-cooling we show an alternative way to eliminate these even at T < Tc. Based on our microwave data, we also determine the critical magnetic field and the critical temperature of Pb in a temperature range between 1.6K and 6.5K and magnetic fields up to 140mT, showing good agreement with BCS predictions. We furthermore study a Sn sample in a Pb resonator to demonstrate the applicability of superconducting Pb stripline resonators in the experimental study of other (super-)conducting materials in a variable magnetic field.

Complete electrodynamics of a BCS superconductor with μeV energy scales: Microwave spectroscopy on titanium at mK temperatures

“…The conductive parts of the resonator, colored black in Fig 1(a), are made of superconducting Pb with a T c ≈ 7.2 K. The center conductor is formed by thermal evaporation using a shadow mask. With pure Pb resonators, where the sample is Pb as well, quality factors exceeding 10 5 can be achieved [53]. The resonator is mounted in a brass box, which is directly connected to the coldfinger of a commercial dilution refrigerator.…”

Microwave probing of bulk dielectrics using superconducting coplanar resonators in distant-flip-chip geometry

“…Planar superconducting microwave resonators play an important role in solid state research, including cryogenic spectroscopic studies. [11][12][13][14][15][16][17][18][19] One can simultaneously probe various harmonics of a fundamental resonance frequency and perform measurements at low temperatures, even in setups with limited space for the sample probe, such as in high magnetic fields or at mK temperatures. 14,[20][21][22][23][24] Superconducting resonators can reach very high quality factors 25 and thus high sensitivity for the dielectric under study.…”

Angle-dependent electron spin resonance of YbRh2Si2 measured with planar microwave resonators and in-situ rotation

“…3 for different sample orientations. Q is generally decreasing with increasing field due to field-induced losses in the superconducting resonator [17,30,31,32,33] and due to the microwave charge response of the heavy fermions [14,26,34,35,36], and additionally it has a dip at the resonance magnetic field B 0 , indicating ESR absorption and thus the spin response of YbRh 2 Si 2 . As can be seen in Fig.…”