Capturing and manipulating dynamic electronic order, phases and couplings in quantum materials
High harmonics are ideal as the illumination source for time- and angle-resolved photoemission spectroscopy (tr-ARPES), which can measure the full electronic band structure of a material. Moreover, a new generation of ultrafast (~50-100 fs), MHz rep rate, VUV (1-20 eV) highly-cascaded high harmonics driven by compact fiber lasers have 10-100 meV energy resolution, and are ideal for spin-resolved ARPES (Optica 7, 832 (2020)).
HHG-based ARPES can not only measure the full electronic band structure - but can also extract the dynamic electron temperature. This measurement capability is very useful since electrons react very quickly upon excitation by light, on attosecond to femtosecond timescales. Moreover, their heat capacity is small compared to the total heat capacity of the material. After excitation by the laser, the excited electrons rapidly establish a hot Fermi-Dirac distribution within ~20 fs. The energy then gradually flows from the hot electrons to the phonon bath on few ps timescales. This decoupling of excitations and interactions in the time domain means that by measuring the dynamic electron temperature, researchers can sensitively detect changes in the microscopic interactions within a material, such as electron-phonon couplings or phase changes – that are indicated by either a change in slope of, or jump in, the electron temperature as a function of excitation laser fluence. When coupled with the ability of HHG tr-ARPES to simultaneously capture the full dynamic band structure (which reflects the macroscopic order parameter), we can map and expand the phase diagram using light as a tuning parameter to uncover new understandings of phase transitions as well as new hidden phases in strongly-coupled materials.
Using this new ultrafast electron calorimetry technique, a number of new observations have been made [1-5]. It has been shown, for example, how ultrafast lasers can be used to delicately manipulate materials properties, to uncover a fundamental new understanding of phase transitions and interactions in strongly-coupled quantum materials. The new behavior observed appears to be universal in many materials and, therefore, opens up routes for coherently manipulating the interactions and properties of 2D and other quantum materials using light. In one finding, a new metastable phase in a charge density wave (CDW) material was uncovered, characterized by a heat capacity of only ~1/3 of the normal material. In another finding, by monitoring the the electron temperature as a function of laser fluence, a new metastable CDW state in 1T-TaSe2 was discovered. In that work, the researchers found that it is possible to manipulate the electron-phonon couplings by varying the laser excitation. They also found that the electron temperature was significantly modulated by the coherent amplitude mode by between 200 and 1000 K - which represents a new discovery, since in all observations to date, the electron temperature in femtosecond-laser-excited systems decreases monotonically as the electron bath loses energy to the lattice.
Y. Zhang, X. Shi, W. You, Z. Tao Y. Zhong, F. Cheenicode Kabeer, P. Maldonado, P. M. Oppeneer, M. Bauer, K. Rossnagel, H. Kapteyn, M. Murnane, "Coherent modulation of the electron temperature and electron-phonon couplings in a 2D material," PNAS 117, 8788 (2020). https://doi.org/10.1073/pnas.1917341117
Xun Shi, Chen-Ting Liao, Zhensheng Tao, Emma Cating, Margaret Murnane, Carlos Hernández-García, Henry Kapteyn, Attosecond light science and its application for probing quantum materials, Invited paper, JPhys Photonics/JPhys B Attosecond focus issue 53, 184008 (2020). https://doi.org/10.1088/1361-6455/aba2fb
X. Shi, W. You, Y. Zhang, Z. Tao, P. Oppeneer, X. Wu, R. Thomale, K. Rossnagel, M. Bauer, H. Kapteyn, M. Murnane, “Ultrafast electron calorimetry uncovers a new long-lived metastable state in 1T-TaSe2 mediated by mode-selective electron-phonon coupling,” Science Advances 5, eaav4449 (2019). DOI: 10.1126/sciadv.aav4449
W. You, P. Tengdin, C. Chen, X. Shi, D. Zusin, Y. Zhang, C. Gentry, A. Blonsky, M. Keller, P. M. Oppeneer, H. Kapteyn, Z. Tao, M. Murnane, “Revealing the nature of the ultrafast magnetic phase transition in Ni by correlating extreme ultraviolet magneto-optic and photoemission spectroscopies,” Physical Review Letters 121, 077204 (2018). DOI: 10.1103/PhysRevLett.121.077204
C. Chen, Z. Tao, A. Carr, P. Matyba, T. Szilvási, M. Piecuch, S. Emmerich, M. Keller, D. Zusin, M. Rollinger, W. You, S. Mathias, U. Thumm, M. Mavrikakis, M. Aeschlimann, P. Oppeneer, H. Kapteyn, M. Murnane, “Distinguishing Attosecond Electron-Electron Scattering and Screening in Transition Metals,” PNAS 114 (27) E5300–E5307 (2017). doi:10.1073/pnas.1706466114
S. Eich, M. Plötzing, M. Rollinger, S. Emmerich, R. Adam, C. Chen, H. Kapteyn, M. Murnane, L. Plucinski, D. Steil, B. Stadtmüller, M. Cinchetti, M. Aeschlimann, C. Schneider, S. Mathias, “Band-structure evolution during the ultrafast ferromagnetic-paramagnetic phase transition in cobalt,” Science Advances 3, e1602094 (2017).
Z. Tao, C. Chen, T. Szilvasi, M. Keller, M. Mavrikakis, H. Kapteyn, M. Murnane, “Influence of the Attosecond Final-state Lifetime on Photoemission from a Transition Metal,” Science 353, 62 (2016). See Science Perspective on this work, Science 353, 28 (2016).
J. Miao, T. Ishikawa, I. K. Robinson & M. M. Murnane, “Beyond Crystallography: Diffractive Imaging with Coherent X-ray Sources,” Science 348, 530 (2015). Featured on cover of Science.
P. Matyba, A. V. Carr, C. Chen, D. L. Miller, G. Peng, S. Mathias, M. Mavrikakis, D. S. Dessau, M. W. Keller, H. C. Kapteyn, and M. M. Murnane, “Controlling the electronic structure of graphene using surface-adsorbate interactions,” Physical Review B Rapid Communication 92, 041407(R) (2015).
L. Yang, G. Rohde, T. Rohwer, A. Stange, K. Hanff, L. Rettig, R. Cortes, F. Chen, D. Feng, T. Wolf, B. Kamble, I. Eremin, T. Popmintchev, M. Murnane,
H. Kapteyn, L. Kipp, J. Fink, M. Bauer, U. Bovensiepen, K. Rossnagel, “Ultrafast modulation of the chemical potential in BaFe2As2 by coherent phonons,” Physical Review Letters 112, 207001 (2014).
S. Eich, A. Stange, A.V. Carr, J. Urbancic, T. Popmintechev, M. Wiesenmayer, K. Jansen, A. Ruffing, S. Jakobs, S. Hellmann, P. Matyba, L. Kipp, K. Rossnagel, M. Bauer, M. M. Murnane, H. C. Kapteyn, S. Mathias, M. Aeschlimann, “Optimizing high-harmonic generation for time- and angle-resolved photoemission spectroscopy using frequency-doubled Ti:sapphire lasers,” Journal of Electron Spectroscopy and Related Phenomena 195, 231–236 (2014).
S. Hellmann, T. Rohwer, M. Kallane, K. Hanff, L. Kipp, T. Carr, M. Murnane, H. Kapteyn, M. Bauer and K. Rossnagel, “Collapsing gaps and dominant interactions in layered charge-density-wave compounds,” Nature Communications 3, 1069 (2012).
L. Miaja-Avila, J. Yin, S. Backus, G. Saathoff, M. Aeschlimann, M. M. Murnane, and H. C. Kapteyn, “Ultrafast Surface Science using the Laser-Assisted Photoelectric Effect with longer-wavelength dressing light,” Physical Review A 79, 030901(R) (2009).
Guido Saathoff, Luis Miaja, Margaret Murnane, Henry Kapteyn, Martin Aeschlimann, “Observation of the Laser-Assisted Photoelectric Effect on Pt(111),” Physical Review A 77, 022903 (2008).
L. Miaja-Avila, G. Saathoff, S. Mathias, J. Yin, C. La-o-vorakiat, M. Bauer, M. Aeschlimann, M. Murnane, H. Kapteyn, “Direct measurement of core-level relaxation dynamics on a surface-adsorbate system,” Physical Review Letters 101, 046101 (2008).
S. Mathias, L. Miaja-Avila, M. M. Murnane, H. Kapteyn, M. Aeschlimann, M. Bauer, “Angle-resolved photoemission spectroscopy with a femtosecond high harmonic light source using a two-dimensional imaging electron analyzer,” RSI 78, 083105 (2007).