CAREER: Discovering and Understanding Layered Nickelate Superconductors

CAREER: Discovering and Understanding Layered Nickelate Superconductors CAREER: Discovering and Understanding Layered Nickelate Superconductors 1. Overview More than a century after its discovery, superconductivity remains one of the most active areas of condensed-matter physics research. The discovery of iron-based superconductors in 2006 reinvigorated the field after intensive exploration of cuprates from the late 1980s. However, pinpointing the mechanism of high-temperature superconductivity (HTS) and determining why the characteristics of HTS materials are so special are fundamental questions yet to be answered. Among myriad approaches to addressing these questions has been the search for cuprate analog materials. After a 30-year quest, the first superconducting nickelate has recently been discovered, hole-doped NdNiO2. This is the first material in a potential new family of unconventional superconductors that are very similar to, yet different from the cuprates. Expanding from a single superconducting material to a new family of nickelate superconductors will be a game changer in the field since 1) it will provide a third example with significant differences and similarities with the known cuprate and iron-based superconducting materials, and 2) it will ultimately provide new insights into the origin of HTS, representing an important step towards a grand unified theory of correlated superconductivity. 2. Intellectual Merit. The explicit goal of this proposal is to discover and establish the theoretical foundations of the first family of nickelate superconductors while addressing their behavior in a microscopic way. This layered nickelate family is represented by the general formula Rn+1(NiO2)nO2 (n= 2, 3, 8, R= rare-earth ion) with each material containing n-NiO2 planes. We will take the only superconducting member as of now, NdNiO2 (n=8), as our poster child since the mechanism giving rise to superconductivity is not yet understood. Our efforts will then extend to explore the potential of other members of the family for superconductivity, with special focus on the currently unexplored n=4-6 materials. The theory approach will run the gamut from fast density functional theory to computationally intensive quasiparticle-self consistent GW+dynamical mean-field theory calculations. With this methodology, we will establish the complexity of the layered nickelate phase diagram, the relationship between competing phases therein and superconductivity, and we will ultimately provide new insights into the nature and origin of HTS. As such, we will be able to address outstanding questions in the field: Can we establish an entire new family of nickelate superconductors rather than finding a single superconducting nickelate? What are the differences and similarities between layered nickelates and cuprates? And, more importantly, what are the relevant cuprate hallmark characteristics that give rise to HTS? 3. Broader Impacts. The discovery of a new family of superconductors will open new venues and lay the foundation of the relevant parameters that give rise to HTS, a defining problem in condensed-matter physics. The proposed studies will give rise to societal benefits by establishing routes to create novel HTS materials- the need for the design and discovery of new superconductors with higher critical temperatures has long been recognized by government reports. This proposal will also establish a novel educational and outreach program focused on broadening participation to bring superconductivity and computational modeling in physics to students and to the general public in metro Phoenix through: i) a summer workshop for high school students from low-income areas and underrepresented groups, ii) an outreach day for high school girls in Hispanic neighborhoods, iii) open house events centered around superconductivity, iv) training next-generation researchers. These outreach and educational efforts will directly benefit the community Arizona State University serves by exposing a wide cross-section of people to exciting aspects of science and by influencing younger generations that generally do not see science career paths represented in their communities.