Observation of supercurrent distribution in YBa2Cu3O7−δ thin films using THz radiation excited with femtosecond laser pulses

Abstract

We have demonstrated that the supercurrent distribution in current-biased YBa2Cu3O7−δ thin films can be obtained by measuring the radiation power of THz electromagnetic pulses excited with femtosecond laser pulses. As the radiation power is proportional to the square of the bias current density at the laser spot position, the two-dimensional current distribution can be obtained from the intensity distribution of THz radiation by scanning the laser spot. The characteristic supercurrent distribution is analyzed by using the critical-state model.

THz beam generation from YBCO thin films using a 1.55 μm femtosecond laser

“…The spot size of the excitation laser was about 25 pm in diameter on the YBCO antenna. The YBCO antenna was mounted on a cold finger of a closed-cycle helium cryostat for supercurrent mapping [9] and kept at 20 K. Using the supercurrent mapping system, the excitation spot on the sample could be easily checked, since we could get the image of the YBCO antenna with a spatial resolution of about 25 pm (see Fig. 3).…”

“…The center wavelength of the exciting laser was 1.55 pm with the average power of 10 mW. The details of the supercurrent mapping have been reported previously[9].…”

Laser terahertz emission microscopy

“…Thus THz emission spectroscopy, as well as THz time domain spectroscopy (THz-TDS), have become important for exploring material science [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. When one excites the THz emission from a certain substance and constructs the emission image by scanning the laser beam on it, the system works as a laser-THz emission microscope (LTEM) [23][24][25][26][27][28][29][30][31][32][33]. Since the resolution of the image is limited by the laser beam diameter rather than THz wavelength, sub-micron resolution images would be easily obtainable.…”

Laser terahertz emission microscope and its application

“…Previously, we proposed LTEM to visualize supercurrent distribution in high-Tc superconductors (HTSCs). 3,4 The maximum amplitude of the radiation emitted from HTSCs is proportional to the real supercurrent density at an optically excited area. Consequently, one can quantify the twodimensional supercurrent density distribution by LTEM.…”