Join us on Thursday, April 25th 2024 for another installment of our Spring Physics Colloquium Series! Our guest lecturer, Dr. Utpal Chatterjee, will be joining us from the University of Virginia!

Abstract: 

Central to the microscopic theory of cuprate high temperature superconductors (HTSCs) is unveiling the low-energy electronic excitations in the pseudogap (PG) phase, where the electronic density of states in the vicinity of the chemical potential is suppressed even above the superconducting (SC) critical temperature (T_c). Theoretical models of the PG phase can be distilled into two broad categories: (i) the PG phase is a precursor to the SC state, and (ii) the PG phase corresponds to some broken symmetry phase that is unrelated to superconductivity. Over the years, Angle Resolved Photoemission spectroscopy (ARPES) and Scanning Tunneling Spectroscopy (STS), which are complementary to each other, have been instrumental in terms of characterizing the single-particle excitations of these materials. These experiments have revealed that, while the electronic states in the vicinity of the zone boundary are gapped below the PG opening temperature T^*, extended regions centered at the zone diagonals, commonly known as the Fermi arcs, are gapless. The mechanism behind Fermi arcs remains one of the most controversial topics in the field. ARPES investigations of the Fermi arcs have predominantly been conducted by focusing directly on the single-particle density of states intensity maps.  The joint density of states patterns, constructed via autocorrelation analysis of ARPES data, can be used to analyze even the subtle details of low-energy electronic excitations both in the PG and SC states. Moreover, thanks to the success of the octet model in the interpretation of the patterns observed in Fourier transform scanning tunneling spectroscopy (FT-STS) data at least in the optimally doped and moderately underdoped samples, the JDOS maps constructed from ARPES data can directly be compared with FT-STS data, facilitating a bridge between real- and momentum-space spectroscopic techniques. Our JDOS studies together with our earlier works on samples in the PG phase of Bi2Sr2CaCu2O8+δ cuprate high temperature superconductors reveal that Fermi arc lengths are indeed temperature (T)- and carrier concentration (δ)-dependent.  Using simulations, based on a broadened superconducting order-parameter scenario for the PG phase, we demonstrate that the PG phase, at least in the moderately underdoped  samples, can be interpreted as a phase incoherent superconducting phase. The natural explanation of δ and T dependence of the Fermi arcs will be as follows: (a) the increase/decrease in Fermi arc length at a fixed δ with increasing/decreasing T is controlled by the imaginary part of the single-particle self-energy Γ(T) and (b) the variation of the Fermi arc length at a fixed T as a function of δ is due an interplay between Γ(T) for 〖T>T〗_c and the strength of the pairing correlations, quantified by the antinodal superconducting energy gap.