Phase competition in trisected superconducting dome (1209.6514v1)

Abstract: A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials such as the cuprate high temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping-and-temperature dependence ARPES study of spectral gaps in Bi$2$Sr$_2$CaCu$_2$O${8+\delta}$ (Bi-2212), covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p$=$0.19 for the pseudogap phase and p$=$0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T$_c$ and exists p$>$0.19 at higher temperatures. Our data imply a revised phase diagram which reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.

• The paper reveals three distinct superconducting regions in Bi-2212, identifying unique gap behaviors and the possibility of two quantum critical points.
• The paper employs comprehensive ARPES measurements to map doping- and temperature-dependent changes in nodal and antinodal gaps, challenging standard models.
• The paper proposes reentrant pseudogap behavior, suggesting that superconducting and pseudogap phases coexist and compete, thus refining the cuprate phase diagram.

Phase Competition in the Trisected Superconducting Dome of Cuprates

The paper "Phase competition in trisected superconducting dome" provides an in-depth examination of the phase transitions in the high-temperature superconducting material Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) using angle-resolved photoemission spectroscopy (ARPES). This research delivers crucial spectroscopic insights into the interplay of the superconductive phase with pseudogap phenomena, revealing what could be two distinct quantum critical points within the superconducting dome, and suggests a revised phase diagram that addresses longstanding conflicts in the literature.

The authors employed ARPES, a powerful technique ideal for studying the anisotropic momentum-space structures of complex materials like the cuprates. The paper presents comprehensive doping- and temperature-dependent studies, revealing three distinct phase regions in the superconducting state of Bi-2212 with unique gap behaviors:

1. Region A (p < 0.076): This region is notable for a fully gapped Fermi surface, contrary to conventional superconductivity in cuprates which is characterized by nodes. Such behavior suggests the emergence of a distinct phase possibly related to spin-density wave order or other complex orders observed in equivalent compounds, like YBa$_2$Cu$_3$O$_y$ (YBCO).
2. Region B (0.076 ≤ p ≤ 0.19): In this region, the gaps near the nodal (NN) and antinodal (AN) points exhibit a remarkable insensitivity to doping, indicating departure from the expected behavior where the nodal gap is correlated with T$_c$. The data propose coexistence of superconductivity and the pseudogap, with distinctive phenomenology manifesting both in doping-independent NN gaps and pseudogapped AN regions extending above T$_c$.
3. Region C (p > 0.19): Representing a transition to more ‘traditional’ superconducting behavior, characterized by diminishing nodal gap values with reducing T$_c$. This region likely heralds the suppression of the pseudogap at sufficiently high doping levels.

One of the compelling contributions of this paper is the proposed reentrant pseudogap behavior within the superconducting dome, suggesting phase competition where the pseudogap may persist at higher temperatures for dopings above the second critical point at p = 0.19. A thorough investigation of gaps above and below T$_c$, along varied dopings, underscores the non-static nature of the pseudogap below T$_c$, an insight critical to understanding cuprate superconductivity.

The paper's implications are multifold. The identification of potential quantum critical points inside the superconducting dome highlights the complexity of the cuprate phase diagram and suggests new directions for theoretical exploration, including the possible coexistence and competition of superconducting and other orders. The concept of reentrant pseudogap behavior introduces pivotal adjustments to existing models of high-temperature superconductivity by necessarily expanding beyond a sole focus on superconducting order.

In conclusion, the findings are poised to significantly influence both experimental research and theoretical modeling of high-temperature superconductivity. As ARPES continues to evolve, offering ever more precise momentum-resolved data, the refinement of phase diagrams such as presented here will pave the way for a deeper microscopic understanding of emergent quantum phases in cuprates, driving forward the broader field of strongly correlated electron systems. Future explorations may explore uncovering the precise mechanisms underpinning these critical points and phase boundaries, potentially unveiling pathways to higher transition temperatures and more robust superconducting states in these enigmatic materials.