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Common Threads in the Electronic Phase Diagram of Unconventional Superconductors
Description and Aim
The last few years have been exceptionally prolific for superconductivity with discoveries of several new materials classes, inventive heterostructures, novel tuning parameters, new intertwined phases (such as charge density wave, nematic order etc), strange metals with or without a critical point at the superconducting dome. These discoveries have helped obtaining higher tunability of the superconducting properties, and new insights which have revived some of the earlier understandings. A basic theme of the workshop is to explore and unify the common properties, combining both earlier and recent results, displayed in all classes of unconventional superconductors including copper-oxides, heavy-fermions, organics, newly discovered iron-pnictide, chalcogenides, and various heterostructures. Such a comprehensive workshop discussing all families together have not much been held earlier, where either focus was given to a given family or different materials were split into parallel sessions.
Unconventional superconductivity is often intervened by correlated physics such as electronic orders and/ or non-Fermi-liquid or strange metal phase, whose nature changes drastically in different materials, making it a difficult problem to solve. We will explore new experimental methods and tunabilities which will enable to individually control the correlated physics and superconductivity with the goal to illuminate how their interplay results in strong Cooper pairing. Experts from all fields will discuss on designing focused experiments which can be carried out in all materials families so that common and important features can be unraveled. Substantial emphasis will be given to utilize the recently developed high-resolution spectroscopies, and multifaceted sample preparation techniques, and multiple tunings methods. An equal focus will be given to the theoretical aspects of both electronic correlation and superconductivity where existing approaches based on strong coupling or weak coupling theories are challenged. A question of general interests is why and how superconductivity often emerges near the boundary between the strong coupling, local and weak coupling, Fermi-liquid like regimes with the cooperation of enhanced non-Fermi liquid physics. We will discuss several newly developed theories for the non-Fermi liquid or strange metal physics without tuning the materials to a quantum critical point. Intermediate coupling (where electronic interaction strength is of the order of bandwidth) models for correlated superconductors, recently observed charge density wave, pair density wave, nematic order for superconductivity, and others will be discussed and confronted with experiments. Given the diversity and versatility of the field, focussed and well-defined problems will be identified where collaborations between experiment and theory can be build and strengthened.
The workshop will be considered a success if leading experts in interdisciplinary fields - both established and young, up-coming scientists – discuss and achieve the following goals:
1) The superconductivity field is quite diverse and has a wide variety of data and hypothesis. Therefore, a key target of the workshop is to discern which properties are common and important for superconductivity, and what are secondary in different families of unconventional superconductors.
2) Followed by it, we will have discussions on focused experiments and theories to solve these canonical problems. We plan to discuss and design new and focused experiments, and samples, heterostructures with enhanced tunability where superconducting and correlated properties can be individually monitored. This will shed light on the interplay between them which promotes strong Cooper pairings. For example, multiple tuning method will be promulgated to all fields to unravel the physics that lie buried under the superconducting dome. Emphasis will be given to those experimental methods which can be performed in a wider classes of materials with different pairing symmetries, superconducting gaps etc., allowing direct comparison between them.
3) In the theoretical side, we will seek to understand why superconductivity arises at the border between strong and weak electronic correlation regimes, and how non-Fermi-liquid physics helps form strong Cooper pair. Identifying the correct correlation strength is an important goal. The underpinnings of the intermediate coupling regime will be discussed in details. Recently, a number of theories proposed the emergence of non-Fermi liquid state without the existence of a quintessential quantum critical point. New experiments also support such hypothesis, providing an entirely new perspective toward the understanding of superconductivity.
4) Strengthen the synergy between theory and experiment to collaboratively study canonical and important problems. The workshop will end with setting deadlines for deliverables, discussion for long-term impacts, and planning for future to assess the progress.