Resume/CV
Here is the PDF version of my CV.pdf. For MS-Word version click CV.doc.
Here is a PDF version of my PhD Thesis.pdf. It’s titled “Evolution of the Excitation Spectrum of Cuprate Superconductors with Doping and Temperature”.
Aakash Pushp
Department of Physics, Princeton University, Princeton, NJ 08544. Email: apushp@princeton.edu
Lab: +1 609 258 9517 Cell: +1 609 356 9785 Homepage: www.princeton.edu/~apushp
Education
University of Illinois, Urbana, IL, USA
PhD in Physics (Supervisor: Prof. Ali Yazdani) 2003-present
University of Illinois, Urbana, IL, USA
Master of Science in Physics 2003-2005
Indian Institute of Technology, Bombay, Mumbai, India
Bachelor of Technology in Engineering Physics 1999-2003
Work Experience
Princeton University, Princeton, NJ, USA
Visiting Student Research Collaborator with Prof. Ali Yazdani 2005-present
Built a Variable Temperature Scanning Tunneling Microscope (VTSTM).
Pivotal in moving and setting up Prof. Yazdani’s lab from Urbana, IL to Princeton, NJ in August 2005.
University of Illinois, Urbana, IL, USA
Teaching Assistant (Undergraduate Electromagnetism) Fall 2003
Chalmers University of Technology, Göteborg, Sweden
Undergraduate summer intern with Prof. Zdravko Ivanov 05/2002 – 07/2002
Topic: Fabrication and Characterization of Tri-layer on a Substrate Slope (ToSS) Josephson Junctions.
Tata Institute of Fundamental Research, Mumbai, India
Undergraduate summer intern with Prof. R. Nagarajan 05/2001 – 07/2001
Topic: Fabrication and Characterization of (Eu,Gd)Sr2Ru1−xCu2+xO8−y Magnetic Superconductors.
Publications
1. Extending Universal Nodal Excitations Optimizes Superconductivity in Bi2Sr2CaCu2O8+δ.
Pushp, A., Parker, C. V., Pasupathy, A., N., Gomes, K. K., Ono, S., Wen, J., Xu, Z., Gu, G., Yazdani, A., Science, 4 June 2009 (10.1126/science.1174338).
2. Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+.
Pasupathy, A. N., Pushp, A., Gomes, K. K., Parker, C. V., Wen, J., Xu, Z., Gu, G., Ono, S., Ando, Y., Yazdani, A., Science 320, 196-201 (11 Apr 2008).
3. Visualizing Pair Formation on the Atomic Scale in the High-Tc Superconductor Bi2Sr2CaCu2O8+.
Gomes, K. K., Pasupathy, A. N., Pushp, A., Ono, S., Ando, Y., Yazdani, A., Nature 447, 569-572 (31 May 2007).
4. Enhancement of Tc in EuSr2Ru1−xCu2+xO8−y Magnetic Superconductor.
Kumar, R., Pushp, A., Tomy, C. V., Nagarajan, R., McK. Paul, D., J. Mag. Mag. Mat. 272, E1073-E1075.
5. Mapping of the formation of the pairing gap in Bi2Sr2CaCu2O8+.
Gomes, K. K., Pasupathy, A. N., Pushp, A., Parker, C. V., Ono, S., Ando, Y., Gu, G., Yazdani, A., J. Phys. Chem. Solids 69 (12) 3034-3038.
6. Gap distributions and spatial variation of electronic states in superconducting and pseudogap states of Bi2Sr2CaCu2O8+.
Gomes, K. K., Pasupathy, A. N., Pushp, A., Ono, S., Ando, Y., Yazdani, A., Physica C: Superconductivity 460 212-215.
Presentations
1.American Physical Society (APS) March Meeting 2009, Pittsburgh, PA, USA
2.Cryoconference 2008, Miraflores de la Sierra, Madrid, Spain
3.25th International Conference on Low Temperature Physics (2008), Amsterdam, The Netherlands
4.American Physical Society (APS) March Meeting 2008, New Orleans, LA, USA
5.Gordon Research Conference on Superconductivity (2007), Les Diablerets, Switzerland
6.American Physical Society (APS) March Meeting 2007, Denver, CO, USA
7.American Physical Society (APS) March Meeting 2006, Baltimore, MD, USA
Research Interests
Experimental Condensed Matter Systems, Scanning Probe Microscopy, Correlated Electron Systems, Low Temperature Physics, High-Temperature Superconductivity, Spintronics.
Recent Research Projects
Visualizing Pair Formation on the Atomic Scale in High-Tc Superconductor Bi2Sr2CaCu2O8+δ
Using variable temperature scanning tunneling spectroscopy (STM), we performed the first spatially resolved measurements of gap formation in a high-Tc superconductor. We found that over a wide range of hole doping, the pairing gaps nucleate in nanoscale regions above Tc. These regions proliferate as the temperature is lowered, resulting in a spatial distribution of gap sizes in the superconducting state. Despite the inhomogeneity, we found that every pairing gap ‘
’ develops locally at a pairing temperature ‘Tp’, following the relation 2
/kBTp=7.9+/-0.5. At very low doping, this relation fails but systematic changes in the density of states (DOS) indicate the presence of distinct physics in this regime, which is likely unrelated and competes with the electron pairing. We found a similar result in the monolayer Bi2Sr2-yLayCuO6 superconductor as well.
Evidence against Electron-Boson Coupling Driving Superconductivity in Bi2Sr2CaCu2O8+δ
Using a lattice-tracking spectroscopy technique with a variable temperature STM, we performed quantitative measurements on the onset of pairing and the boson exchange mechanism in Bi2Sr2CaCu2O8+δ. In this quest, the challenge was to perform DOS measurements both in the normal and the superconducting state while tracking the same atomic lattice sites. Analysis of the data showed no correlation between the inhomogeneous pairing gaps and either the energy scale of the boson modes or the strength of the local electron-boson coupling as measured by the local DOS. Thus, electron-boson coupling in the range of 20 to 120 meV cannot be responsible for pair formation.
Electronic Origin of the Inhomogeneous Pairing Interaction in Bi2Sr2CaCu2O8+δ
In search of a better candidate for the pairing interactions, we performed local measurements in the normal as well as superconducting state of the same nanoscale area of the sample. This revealed that the DOS in the normal state near the Fermi energy strongly anti-correlates with the inhomogeneous pairing gap in the superconducting state. This anti-correlation runs contrary to a BCS-like pairing mechanism, where the coupling to bosons is proportional to the DOS at the Fermi energy. Instead, unusual electronic excitations of the normal state determine the strength of pairing, which suggests that strong electron-electron interactions are responsible for superconductivity in the cuprates.
Universal Nodal Excitations and Underlying Mechanism for Optimal Superconductivity in Bi2Sr2CaCu2O8+δ
Understanding the mechanism by which d-wave superconductivity in the cuprates emerges and is optimized by doping the Mott insulator is one of the major outstanding problems in condensed matter physics. Our high-resolution scanning tunneling microscopy measurements of the high transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ show that samples with different Tcs in the low doping regime (0.07 < x < 0.15) follow a remarkably universal d-wave low energy excitation spectrum, indicating a doping independent nodal gap. We demonstrate that Tc correlates with the fraction of the Fermi surface over which the samples exhibit the universal spectrum. Optimal Tc is achieved when all parts of the Fermi surface follow the universal behavior. Increasing temperature above Tc turns the universal spectrum into an arc of gapless excitations, while overdoping breaks down the universal nodal behavior.
Evolution of Quasi-Particle Interference and Two Energy Features in Under-doped Bi2Sr2CaCu2O8+δ
We are currently working on bringing out the connection between dispersive real space modulations of the DOS observed in the deeply superconducting phase and the non-dispersive real space modulations observed in the Pseudogap phase. We are investigating the nature of this crossover in the modulations and its correlation with the Tc of the sample.
References
Prof. Ali Yazdani
Department of Physics
Princeton University
Princeton, NJ, USA
Prof. Abhay Pasupathy
Department of Physics
Columbia University
New York, NY, USA
Prof. D. Van Harlingen
Department of Physics
University of Illinois
Urbana, IL, USA