NMU Physics: Assistant Professor

Winter 2017: College Physics I: Lab (General Info for all lab sections) [NOTE: Dr. Mengyan's section has more detailed and section specific information available via EduCat]

Winter 2017: Modern Physics Lecture and Lab (PH 322: MWF 14:00 to 14:50, R 14:00 to 16:50) [Course material available via EduCat, linked here]

Fall 2016: College Physics 1 Lecture (MWRF 14:00 to 14:50)

Fall 2016: College Physics 1 Lab (-03,-04,-08)

Courses below here were taught at Texas Tech University

Summer 2016: Senior Project (Physics major, PHYS 4306)

Winter 2016: Undergraduate Research (Experimental solid-state physics, PHYS 3000)

Winter 2016: Principles of Physics I [Calculus-based] (PHYS 1408-001 CRN: 45473 and 1408-004 CRN: 54556)

Winter 2016: Intermediate Physics Lab (PHYS 3304 CRN: 46372)

Fall 2015: Undergraduate Research (Experimental solid-state Physics, PHYS 3000)

Fall 2015: Principles of Physics I [Calculus-based] (PHYS 1408-003 CRN: 29508)

Summer 2015: Undergraduate Research (Experimental solid-state physics, PHYS 3000)

Winter 2015: General Physics I [Algebra-based] (PHYS 1403-002 CRN: 40292)

Winter 2015: Intermediate Physics Lab (PHYS 3304 CRN: 46372)

Fall 2014: General Physics I [Algebra-based] (Phys 1403-001)

Research Interests

My field is experimental condensed matter Physics. I am currently working on a few projects and one interest resides in the investigation of the microscopic distribution of magnetic fields within magnetic semiconducting materials with the prospects of potential applications in spin electronics. During the course of this particular investigation, we have found evidence of, what we believe to be, spin polarons in several types of magnetic materials as well as some superconducting materials. Some preliminary results seem to suggest that the spin polaron may be directly related various exotic magnetic ordering (ie. helical, etc) or give rise to other unique properties such as magnetoresistive behavior, metal to insulator transitions and, in some cases, superconductivity. The primary focus of my Ph.D. work was in dilute magnetic semiconducting systems and their parent compounds; specifically the investigation of the magnetic features in Mn doped II-IV-V2 chalcopyrites (such as ZnGeP2:Mn) as well as the Mn doped II-VI compounds (such as (Cd,Mn)Te). With a combination of MuSR measurements, neutron scattering and bulk magnetiztation (SQUID and AGM) measurements, we have determined that spin polarons likely provide the transfer of magnetism from local moments (Mn) to the charge carriers (holes) for which neither of the limiting cases for more standard theories seem to apply. (Link to dissertation: Magnetism in Mn-Doped Chalcopyrites).

Another current project is focused on probing the magnetism, metal to semiconductor transition and properties of hydrogen in vanadium dioxide (VO2) compounds, via MuSR and neutron scattering. The focus of this project is to characterize the local electronic and magnetic environment in a variety of VO2 compounds where the implanted muon acts as both an experimentally accessible analog to hydrogen and a very sensitive probe of the local magnetic environment. While still in the early stages, preliminary results show a never before detected (to our knowledge) low temperature magnetic phase in VO2 compounds (investigated thus far: VO2, VO2:Ti, VO2:W) where the onset temperature is significantly higher in the doped materials. This project aims to identify the source of the magnetic phase, characterize the muon/Hydrogen behavior and provide insight into the highly debated source of the metal to semiconductor transition (including both structural and electronic components) occurring near room temperature and can be tuned by adjusting the type and concentration of the dopants. An additional goal is to determine the particular role that the dopants play in modifying these transitions and related material properties. (Manuscripts are in preparation).

The main research technique that our group utilizes is MuSR, where the 'R' stands for 'Research', 'Rotation', 'Resonance' or 'Relaxation' depending on the specific application of the technique as being discussed. Basically, we implant 100% spin polarized muons into a sample and monitor how they interact with the host system based on the decay signature [e.g see: J.H. Brewer, et al, "Mu+SR Spectroscopy: The Positive Muon as a Magnetic Probe in Solids", Physica Scripta 11 (1974) 144-148]. This technique has a wide range of applications beyond being a very sensitive probe of the magnetic environment, including the ability to use Muonium (muon that has captured an electron) to study Hydrogen-like defect centers in semiconducting materials or a tool to study the Hydrogen atom chemistry in reactions that would be otherwise unobservable. Additionally, the MuSR technique can probe the superconducting properties such as the radii of vortex cores, coherence lengths and penetration depths. Other applications of the MuSR technique as well as additional information regarding this experimental method can be found on http://musr.ca.
The bulk of my research is carried out at two of the four MuSR facilities, world-wide; TRIUMF located in Vancouver, BC and the STFC ISIS facility at Rutherford Appleton Lab located in Oxfordshire, UK. Independent of my MuSR work, I have also participated in neutron scattering work at Oak Ridge National Laboratory (PI: Dr. B.R. Carroll of Arkansas State University) to further investigate some of the magnetic properties of the Mn-doped chalcopyrite systems.
Many of the projects in which I am actively involved are part of collaborations with R.L. Lichti (Texas Tech), R.C. Vilao's group (University of Coimbra, Portugal), B.B. Baker (Francis Marion University, SC), Y.G. Celebi (Istanbul University, Turkey), J.H. Brewer (University of British Columbia and TRIUMF, Canada), V.G. Storchak (Kurchatov Institute, Russia), J.S. Lord (Rutherford Appleton Lab, UK), K. Yokoyama (Rutherford Appleton Lab, UK), A.J. Drew (Queen Mary University of London, UK) and B.R. Carroll (Arkansas State University, USA).

Book Chapter:

The role of muons in semiconductor research
P.W. Mengyan. in Characterisation and control of defects in semiconductors. ed. F. Tuomisto (IET: London, 2019). Hardcover ISBN 978-1-78561-655-6 .

Selected Publications:

Modelling isolated hydrogen impurity in Lu2O3 with muonium spectroscopy.
R.C. Vilao, R.B.L. Vieira, H.V. Alberto, J.M. Gil, A. Weidinger, R.L. Lichti, P.W. Mengyan, B.B. Baker and J.S. Lord. EPJ 223 (2020) 04001.

Optical spectroscopy of muon/hydrogen defects in 6H-SiC.
J.S. Lord, K. Yokoyama, P.W. Mengyan, M.R. Goeks, R.L. Lichti, R.C. Vilao and H.V. Alberto J Appl Phys 127 (2020) 095702.

Muon probes of temperature-dependent charge carrier kinetics in semiconductors.
K. Yokoyama, J.S. Lord, P.W. Mengyan, M.R. Goeks and R.L. Lichti Appl Phys Lett 115 (2019) 112101.

Barrier model in muonium implantation and application to Lu2O3.
R.C. Vilao, R.B.L. Vieira, H.V. Alberto, J.M. Gil, A. Weidinger, R.L. Lichti, P.W. Mengyan, B.B. Baker and J.S. Lord Phys Rev B 98 (2018) 115201 .

Dynamics of heavy carriers in the ferromagnetic superconductor UGe2.
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, O.E. Parfenov, and A.M. Tokmachev. JETP Letts 107 (2018) 470.

Coupling of magnetic orders in La2CuO(4+x).
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, O.E. Parfenov, A.M. Tokmachev and P. Dosanjh. Phys Rev B 94 (2016) 134407 .

Isolated Hydrogen configurations in zirconia as seen by muon spin spectroscopy and ab-initio calculations.
R.B.L. Vieira, R.C. Vilao, V.G. Marinopoulos, P.M. Gordo, J.A. Paixao, H.V. Alberto, J.M. Gil, A. Weidinger, R.L. Lichti, B.B. Baker, P.W. Mengyan and J.S. Lord. Phys Rev B 94 (2016) 115207

Spin gap in heavy fermion compound UBe13.
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, O.E. Parfenov, A.M. Tokmachev, P. Dosanajh, Z. Fisk, J.L. Smith. N Journ Phys 18 (2016) 83029.

Electronic Structure of Interstitial Hydrogen in Lutetium Oxide from DFT+U Calculations and Comparison Study with MuSR Spectroscopy .
E. Lora da Silva, A.G. Marinopoulos, R.B.L. Vieira, R.C. Vilao, H.V. Alberto, J.M. Gil, R.L. Lichti, P.W. Mengyan, B.B. Baker. Phys Rev B 94 (2016) 014104.

The muonium donor in TiO2 and comparison with hydrogen .
R.C. Vilao, R.B.L. Vieira, H.V. Alberto, J.M. Gil, A. Weidinger, R.L. Lichti, B.B. Baker, P.W. Mengyan and J.S. Lord. Phys Rev B 92 (2015) 081202(R).

Intra-unit-cell magnetic order in stoichiometric La2CuO4.
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, O.E. Parfenov, A.M. Tokmachev, P. Dosanjh and S.N. Barilo. Phys Rev B 91 (21 May 2015) 205122.

Spectroscopic identification of shallow muonium acceptors in Si0.06Ge0.94.
B.R. Carroll, R.L. Lichti, P.W. Mengyan, B.B. Baker, Y.G. Celebi, P.J.C. King, K.H. Chow and I. Yonenaga. Appl Phys Lett 105 (2014) 122101.

Magnetic order and muon motion in VO2 .
P.W. Mengyan, R.L. Lichti, B.B. Baker and G. Jayarathna. J Phys: Conf Ser 551 (2014) 012017.

Local magnetic order in La2CuO4 seen via mu+SR spectroscopy.
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, O.E. Parfenov, A.M. Tokmachev, P. Dosanjh and S.N. Barilo. J Phys: Conf Ser 551 (2014) 012024.

Spin-polaron band in the ferromagnetic heavy-fermion superconductor UGe2.
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, O.E. Parfenov and D. Sokolov. J Phys: Conf Ser 551 (2014) 012016.

Search for ALCR-Mu+SR spin polaron resonances in Cd2Re2O7 and FeGa3.
J.H. Brewer, V.G. Storchak, D.G. Eshchenko, R.L. Lichti, P.W. Mengyan and D.J. Arseneau. J Phys: Conf Ser 551 (2014) 012022.

High field study of muonium states in HfO2 and ZrO2.
R.B.L. Vieira, R.C. Vilao, H.V. Alberto, J.M. Gil, A. Weidinger, B.B. Baker, P.W. Mengyan and R.L. Lichti. J Phys: Conf Ser 551 (2014) 012048.

Magnetic fields and fluctuations in weakly Mn doped ZnGeP2 .
P.W. Mengyan, R.L. Lichti, Y.G. Celebi, B.B. Baker, B.R. Carroll, E. Catak, K.T. Zawilski and P.G. Schunenmann. AIP Conf Proc 1583 (2014) 190.

Transition dynamics for Mu acceptor centers in Si(1-x)Ge(x) alloys.
G. Jayarathna, R.L. Lichti, P.W. Mengyan, Y.G. Celebi, B.B. Baker, B.R. Carroll and I. Yonenaga. AIP Conf Proc 1583 (2014) 56.

Motional characteristics of positively charged muonium defects in In2O3.
B.B. Baker, Y.G. Celebi, R.L. Lichti, P.W. Mengyan and E. Catak. AIP Conf Proc 1583 (2014) 323.

Observation of magnetic polaron in the magnetoresistive pyrochlore Lu2V2O7 .
V.G. Storchak, J.H. Brewer, D.G. Eshchenko, P.W. Mengyan, H. Zhou and C.R. Wiebe. Journal of Physics: Condensed Matter 25 (2013) 115601.

Antiferromagnetism in the spin-gap system NaV2O5: Muon spin rotation measurements.
V.G. Storchak, O.E. Parfenov, D.G. Eshchenko, R.L. Lichti, P.W. Mengyan, M. Isobe and Y. Ueda. Phys Rev B 85 (2012) 094406.

Muonium Transitions in Si-Ge Alloys.
P.W. Mengyan, R.L. Lichti, Y.G. Celebi, B.R. Carroll, B.B. Baker, H.N. Bani-Salameh, I. Yonenaga. Physica B: Condensed Matter. 407 (2012) 2829-2832.

Motion of Positively Charged Muonium in ZnO.
B.B. Baker, Y.G. Celebi, R.L. Lichti, P.W. Mengyan, H.N. Bani-Salameh, B.R. Carroll. Physica B: Condensed Matter. 407 (2012) 2864-2866.

Muonium Dynamics in Transparent Conducting Oxides.
Y.G. Celebi, R.L. Lichti, B.B. Baker, P.W. Mengyan, H.N. Bani-Salameh. Physica B: Condensed Matter. 407 (2012) 2879-2882.

Longitudinal Muon Spin Depolarization in Ge-Rich SiGe Alloys.
P.W. Mengyan, Y.G. Celebi, R.L. Lichti, B.R. Carroll, B.B. Baker, H.N. Bani-Salameh, I. Yonenaga. Physica Procedia 30 (2012) 214-218.

Spin Polarons in Strongly Correlated Electron Materials.
V.G. Storchak, O.E. Parfenov, J.H. Brewer, D.G. Eshchenko, R.L. Lichti, P.W. Mengyan, D.J. Arseneau, B. Hitti. Physica Procedia 30 (2012) 178-181.

Initial Study of Positively Charged Muonium Motion in ZnO, CdO, TiO₂ and SnO₂.
B.B. Baker, Y.G. Celebi, R.L. Lichti, P.W. Mengyan, H.N. Bani-Salameh, B.R. Carroll. Physica Procedia 30 (2012) 101-104.

Motion of Mu⁺ in Transparent Conducting Oxides.
Y.G. Celebi, R.L. Lichti, B.B. Baker, P.W. Mengyan, H.N. Bani-Salameh. Physica Procedia 30 (2012) 206-209.

Spin Polarons in the Correlated Metallic Pyrochlore Cd2Re2O7.
V.G. Storchak, J.H. Brewer, S.L. Stubbs, O. E. Parfenov, R.L. Lichti, P.W. Mengyan, J.He, I.Bredeson, D. Hitchcock and D. Mandrus. Phys Rev Lett. 105 (2010) 076402.

Hyperfine Spectroscopy and Characterization of Muonium in ZnGeP2.
P.W. Mengyan, B.B. Baker, R.L. Lichti, K.H. Chow, Y.G. Celebi, K.T. Zawilski and P.G. Schunemann. Physica B: Condensed Matter. 404 (2009) 5121-5124.

Selected Research Presentations (Primary Author):

Muonium in anatase and brookite TiO₂.
(2019: 30^th International Conference on Defects in Semiconductors. Seattle, Washington USA)

Muonium as H in Brookite TiO2₂.
(2018: Gordon Research Conference on Defects in Semiconductors. New London, NH)

A First look at Mu in Anatase TiO₂.
(2017: 14^th International Conference on Muon Spin Rotation, Relaxation and Resonance. Sapporo, Japan)

Role of the Muon in Semiconductor Research.
(2017, Invited Talk: March 2017 Meeting of the American Physical Society. New Orleans, LA)

Magnetism and Mu Dynamics in VO₂ Compounds.
(2015, Corbett Prize Finalist Presentation: 28th International Conference on Defects in Semiconductors. Espoo, Finland)

Magnetism and Mu Dynamics in Vanadium Dioxide Compounds.
(2014, Talk: TTU Department of Physics Colloquium. Lubbock, TX)

Magnetic Order and Muon Motion in VO₂ Compounds
(2014, Poster: Gordon Research Conference: Defects in Semiconductors. Waltham, MA)

Magnetic Order and Muon Motion in Pure VO₂.
(2014, Talk: 13^th International Conference on Muon Spin Rotation, Relaxation and Resonance. Grindelwald, Switzerland)

Magnetic Fluctuations in ZnGeP₂:Mn
(2013, Poster: International Conference on Defects in Semiconductors, ICDS-27. Bologna, Italy)

Probing Local Features in Dilute Magnetic Semiconducting ZnGeP₂:Mn via Mu⁺SR
(2012, Poster: Joint Fall Meeting Texas Section of APS, AAPT and Zone 13 SPS. Lubbock, TX)

Probing Local Features in Dilute Magnetic Semiconducting ZnGeP₂:Mn via Mu⁺SR
(2012, Poster: Gordon Research Conference: Defects in Semiconductors. Biddeford, ME)

Probing the Internal Magnetic Field Features of the II-IV-V₂:Mn DMS via MuSR
(2012, Talk: Joint Spring 2012 Meeting of the Texas Sections of the APS, AAPT and Zone 13 of the SPS. San Angelo, TX)

Muonium Transitions in Ge-rich SiGe Alloys
(2011, Talk: International Conference on Defects in Semiconductors, ICDS-26. Nelson, New Zealand)

Longitudinal Muon Spin Depolarization in Bulk Si_0.09Ge_0.91
(2011, Poster: 12^th International Conference on Muon Spin Rotation, Relaxation and Resonance. Cancun, Mexico)

Observing Spin Polarons in Magnetic Semiconducting and Various Other Materials via Mu+SR
(2010, Poster: Gordon Research Conference: Defects in Semiconductors. New London, NH)

Hyperfine Spectroscopy and Characterization of Muonium Centers in ZnGeP₂
(2009, Talk: Texas Section APS Meeting. San Marcos, TX)

Hyperfine Spectroscopy and Characterization of Muonium in ZnGeP₂
(2009, Poster: ICDS-25. St. Petersburg, Russia)

Selected Student Research Presentations:

Characterization of the Magnetic Phase in Ti-Doped Vanadium Dioxide.
M.R. Goeks, P.W. Mengyan, R.L. Lichti. (2018: APS Conference for Undergraduate Women in Physics. Toledo, OH)

Characterizating the Muonium Impurity in Anatase TiO₂.
J.A. Horn, P.W. Mengyan, R.L. Lichti, J.S. Lord. (2017: National Ronald E. McNair Research Conference. Schaumburg, IL)

Select Awards

April 2016: Professor of the Year in Physics (Texas Tech University, Physics)

July 2015: Corbett Prize Finalist (28th International Conference on Defects in Semiconductors. Espoo, Finland)

June 2014: Young Scientist Award. (International Society for Muon Spectroscopy, ISMS)

May 2014: Outstanding Ph.D. (TTU Department of Physics).