Rapid change of superconductivity and electron-phonon coupling through critical doping in Bi-2212

Abstract

Electron-boson coupling plays a key role in superconductivity for many systems.However, in copper-based high-temperature (Tc) superconductors, its relation to superconductivity remains controversial despite strong spectroscopic fingerprints. Here we use angle-resolved photoemission spectroscopy to find a striking correlation between the superconducting gap and the bosonic coupling strength near the Brillouin zone boundary in Bi2Sr2CaCu2O8+δ. The bosonic coupling strength rapidly increases from the overdoped Fermi-liquid regime to the optimally doped strange metal, concomitant with the quadrupled superconducting gap and the doubled gap-to-Tc ratio across the pseudogap boundary. This synchronized lattice and electronic response suggests that the effects of electronic interaction and the electron-phonon coupling re-enforce each other in a positive feedback loop upon entering the strange metal regime, which in turn drives a stronger superconductivity.Main Text: The phase diagram of cuprate high temperature superconductors hosts a number of complex orders, types of fluctuations and interactions (1 -4). In the non-Fermi liquid strange metal regime, a hierarchy of microscopic interactions are intimately at play but not fully understood (1,2,4). Although the experimental evidence for d-wave superconductivity (5 -7) naturally points to an electron-electron interaction based pairing mechanism (8 -12), the omnipresent charge order (3) points to the role of electron-phonon coupling (EPC), especially in a new context of enhanced EPC by electronic correlation (13,14) and multichannel boosted superconductivity (15 -17).Although there have been reports of EPC imprinting on the electronic structure of many cuprate superconductors (18 -21), little evidence directly correlates EPC with the intertwined orders in the phase diagram (1 -2). Focusing on the overdoped side in Bi2Sr2CaCu2O8+δ (Bi-2212), we find via angle-resolved photoemission spectroscopy (ARPES) a set of striking effects rapidly crossing

Experimental Determination of Momentum-Resolved Electron-Phonon Coupling

“…In conventional superconductors, the EPC drives the formation of bosonic bound states of electrons (the Cooper pairs) [1]. In unconventional superconductors such as copper oxides (cuprates), the role of the EPC is lively discussed [2][3][4][5][6][7][8][9][10][11]. Though a purely phonon-mediated mechanism cannot account for the high critical temperatures observed in doped cuprates, the electron-lattice interaction may enhance pair binding when it operates in synergy with a dominant mechanism [12][13][14][15][16][17].…”

Mode-Selective Coupling of Coherent Phonons to the Bi2212 Electronic Band Structure

“…Combining the electron energy shift and the lattice distortion defines a coherent "lock-in" experiment which determines the deformation potential purely experimentally [31]. Furthermore, improvements of the time resolution will grant access to other important modes, in particular the 8.5 THz B 1g mode [20][21][22]62] and the 17 THz apical mode [63]. These experimental pursuits will be vital for theories examining the complex interactions underlying high temperature superconductivity.…”

Distinct Superconducting Gap on Two Bilayer-Split Fermi Surface Sheets in Bi2Sr2CaCu2O8+δ Superconductor*

“…In the underdoped region, the normal state deviates significantly from the Fermi liquid behaviors and the superconducting gap is particularly anomalous: it decreases with increasing doping even though T c still increases with doping, and the measured momentumdependent superconducting gap deviates more obviously from the standard d-wave form with decreasing doping [1,2,4,5]. In the overdoped region, on the other hand, the normal state properties appear to become close to a Fermi liquid while the superconducting gap tends to resemble the BCS behaviors: it decreases with increasing doping with a concomitant T c decrease and its momentum dependence follows a standard d-wave form [1,2,5,6]. It has been also found that superconductivity of the cuprate superconductors is sensitive to the number of CuO 2 planes, n, in one structural unit; T c increases from single-layer (n=1), to bilayer (n=2) and trilayer (n=3), reaches a maximum for trilayer (n=3), and then drops with the further increase of the number of CuO 2 planes [7][8][9].…”

“…It has been also found that superconductivity of the cuprate superconductors is sensitive to the number of CuO 2 planes, n, in one structural unit; T c increases from single-layer (n=1), to bilayer (n=2) and trilayer (n=3), reaches a maximum for trilayer (n=3), and then drops with the further increase of the number of CuO 2 planes [7][8][9]. Investigations on the doping dependence and CuO 2 layer dependence of the electronic structure and superconducting gap symmetry are important for understanding the origin of high temperature superconductivity in cuprate superconductors Angle-resolved photoemission spectroscopy (ARPES) measurements on Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) have provided major results on the doping and temperature evolutions of electronic structure, many-body effects, peudogap and superconducting gap about cuprate superconductors [1,2,5,6,10,11] because Bi2212 is easy to cleave to get smooth sample surface for ARPES measurements and can cover a relatively wide range of doping levels. In fact, Bi2212 consists of two CuO 2 planes in one structural unit separated by calcium (Ca).…”